DEV Community: Rui Kowase

LeetCode in Kotlin: 20. Valid Parentheses

Rui Kowase — Mon, 08 Apr 2019 10:33:55 +0000

Problem

https://leetcode.com/problems/valid-parentheses/

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.

Example:

Input: "()"
Output: true
Example 2:

Input: "()[]{}"
Output: true
Example 3:

Input: "(]"
Output: false
Example 4:

Input: "([)]"
Output: false
Example 5:

Input: "{[]}"
Output: true

Solution

fun isValid(s: String): Boolean {
    val stack = Stack<Char>()

    val map = mapOf(
        '}' to '{',
        ')' to '(',
        ']' to '['
    )

    s.forEach {
        stack.push(it)

        if (map.containsKey(it)) {
            if (stack.size < 2) {
                return false
            }

            if (stack[stack.size - 2] != map[it]) {
                return false
            }

            stack.pop()
            stack.pop()
        }
    }

    return stack.isEmpty()
}

fun isValid(s: String): Boolean {
    val stack = Stack<Char>()
    val range = (1..2)
    s.forEach { c ->
        when {
            stack.empty() -> stack.push(c)
            (c - stack.peek()) in range -> stack.pop()
            else -> stack.push(c)
        }
    }
    return stack.empty()
}

fun isValid(s: String): Boolean {
    val stack = Stack<Char>()
    val map = mapOf(
        '(' to ')', ')' to '(',
        '[' to ']', ']' to '[',
        '{' to '}', '}' to '{'
    )
    s.forEach { c ->
        when {
            stack.empty() -> stack.push(c)
            stack.peek() == map[c] -> stack.pop()
            else -> stack.push(c)
        }
    }
    return stack.empty()
}

Test code

@Test
fun isValid() {
    assertTrue(solution.isValid("()"))
    assertTrue(solution.isValid("[]"))
    assertTrue(solution.isValid("{}"))
    assertTrue(solution.isValid("{()}"))
    assertTrue(solution.isValid("{([])}"))
    assertFalse(solution.isValid("{{"))
    assertFalse(solution.isValid("{)"))
    assertFalse(solution.isValid(")"))
    assertFalse(solution.isValid(")("))
}

Model solution

https://leetcode.com/problems/valid-parentheses/solution/

Approach 1: Stacks

class Solution {

  // Hash table that takes care of the mappings.
  private HashMap<Character, Character> mappings;

  // Initialize hash map with mappings. This simply makes the code easier to read.
  public Solution() {
    this.mappings = new HashMap<Character, Character>();
    this.mappings.put(')', '(');
    this.mappings.put('}', '{');
    this.mappings.put(']', '[');
  }

  public boolean isValid(String s) {

    // Initialize a stack to be used in the algorithm.
    Stack<Character> stack = new Stack<Character>();

    for (int i = 0; i < s.length(); i++) {
      char c = s.charAt(i);

      // If the current character is a closing bracket.
      if (this.mappings.containsKey(c)) {

        // Get the top element of the stack. If the stack is empty, set a dummy value of '#'
        char topElement = stack.empty() ? '#' : stack.pop();

        // If the mapping for this bracket doesn't match the stack's top element, return false.
        if (topElement != this.mappings.get(c)) {
          return false;
        }
      } else {
        // If it was an opening bracket, push to the stack.
        stack.push(c);
      }
    }

    // If the stack still contains elements, then it is an invalid expression.
    return stack.isEmpty();
  }
}

LeetCode in Kotlin: 7. Reverse Integer

Rui Kowase — Mon, 08 Apr 2019 10:27:21 +0000

Problem

https://leetcode.com/problems/reverse-integer/

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321
Example 2:

Input: -123
Output: -321
Example 3:

Input: 120
Output: 21

Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

Solution

fun reverse(x: Int): Int {
    val str = x.toString()
    val stack = Stack<Char>()
    var result = ""

    str.forEach {
        stack.push(it)
    }

    while (true) {
        if (stack.size == 0) break

        if (result.isEmpty() && stack.peek() == '0') {
            if (stack.size == 1) {
                result = "0"
                break
            }

            stack.pop()
            continue
        }

        if (stack.peek() == '-') {
            result = stack.peek() + result
            break
        }

        result += stack.pop()
    }

    return try {
        result.toInt()
    } catch (e: NumberFormatException) {
        0
    }
}

fun reverse(x: Int): Int {
    val output = StringBuilder()
    var currVal = x

    if (currVal < 0) {
        currVal *= -1
        output.append("-")
    }

    output.append(currVal.toString().reversed())

    return output.toString().toIntOrNull() ?: 0
}

fun reverse(x: Int): Int {
    val y = abs(x)
        .toString()
        .reversed()
        .toIntOrNull() ?: return 0

    return when {
        0 <= x -> y
        else -> y * -1
    }
}

Test code

@Test
fun reverse() {
    assertEquals(321, solution.reverse(123))
    assertEquals(-321, solution.reverse(-123))
    assertEquals(21, solution.reverse(120))
    assertEquals(21, solution.reverse(1200))
    assertEquals(0, solution.reverse(0))
    assertEquals(0, solution.reverse(1534236469))
}

Model solution

https://leetcode.com/problems/reverse-integer/solution/

Approach 1: Pop and Push Digits & Check before Overflow

class Solution {
    public int reverse(int x) {
        int rev = 0;
        while (x != 0) {
            int pop = x % 10;
            x /= 10;
            if (rev > Integer.MAX_VALUE/10 || (rev == Integer.MAX_VALUE / 10 && pop > 7)) return 0;
            if (rev < Integer.MIN_VALUE/10 || (rev == Integer.MIN_VALUE / 10 && pop < -8)) return 0;
            rev = rev * 10 + pop;
        }
        return rev;
    }
}

LeetCode in Kotlin: 1. Two Sum

Rui Kowase — Mon, 08 Apr 2019 10:20:03 +0000

Problem

https://leetcode.com/problems/two-sum/

Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Solution

fun twoSum(nums: IntArray, target: Int): IntArray {
    for (i in 0 until nums.size) {
        for (j in i + 1 until nums.size) {
            if (nums[i] + nums[j] == target) {
                return intArrayOf(i, j)
            }
        }
    }

    throw IllegalArgumentException("No solution")
}

fun twoSum(nums: IntArray, target: Int): IntArray {
    val map = HashMap<Int, Int>()
    nums.forEachIndexed { idx, item ->
        val found = map[target - item]
        found?.let {
            return intArrayOf(found, idx)
        }
        map[item] = idx
    }
    throw IllegalArgumentException("No solution")
}

Test code

@Test
fun twoSum() {
    t(intArrayOf(2, 7, 11, 15), 9, intArrayOf(0, 1))
    t(intArrayOf(3, 2, 4), 6, intArrayOf(1, 2))
}

private fun t(nums: IntArray, target: Int, expected: IntArray) {
    val actual = solution.twoSum(nums, target)

    assertEquals(expected.size, actual.size)
    expected.forEachIndexed { index, i ->
        assertEquals(expected[index], i)
    }
}

Model solution

https://leetcode.com/problems/two-sum/solution/

Approach 1: Brute Force

public int[] twoSum(int[] nums, int target) {
    for (int i = 0; i < nums.length; i++) {
        for (int j = i + 1; j < nums.length; j++) {
            if (nums[j] == target - nums[i]) {
                return new int[] { i, j };
            }
        }
    }
    throw new IllegalArgumentException("No two sum solution");
}

Approach 2: Two-pass Hash Table

public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
        map.put(nums[i], i);
    }
    for (int i = 0; i < nums.length; i++) {
        int complement = target - nums[i];
        if (map.containsKey(complement) && map.get(complement) != i) {
            return new int[] { i, map.get(complement) };
        }
    }
    throw new IllegalArgumentException("No two sum solution");
}

Approach 3: One-pass Hash Table

public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
        int complement = target - nums[i];
        if (map.containsKey(complement)) {
            return new int[] { map.get(complement), i };
        }
        map.put(nums[i], i);
    }
    throw new IllegalArgumentException("No two sum solution");
}

[Android] How to mock final class with Mockito2

Rui Kowase — Wed, 13 Feb 2019 14:56:16 +0000

In Android project, data class is final. So final class can't be extended.

Issue

This error will be happen when data class is mocked by using mock(), spy(), etc...

org.mockito.exceptions.base.MockitoException: 
Cannot mock/spy class net.kikuchy.example.ComplexData
Mockito cannot mock/spy because :
 - final class

Solution

Adding mockito-inline

dependencies {
    testImplementation "org.mockito:mockito-core:$mockito_version"
    testImplementation "org.mockito:mockito-inline:$mockito_version"
}

How to generate Flutter app icons for iOS and Android

Rui Kowase — Sun, 01 Apr 2018 15:01:39 +0000

TL;DR

Use flutter_launcher_icons that Command line tool.

Environment

Flutter 0.1.5
Dart 2.0.0-dev.28.0
flutter_launcher_icons 0.2.0

How to create

1. Add `flutter_launcher_icons` Plugin

Add flutter_launcher_icons to pubspec.yaml

dev_dependencies: 
  flutter_test:
    sdk: flutter

  flutter_launcher_icons: "^0.2.0"

flutter_icons:
  image_path: "icon/icon.png" 
  android: true
  ios: true

2. Prepare app icon

Prepare an app icon for the specified path.
e.g. icon/icon.png

3. Create app icons

Execute this on terminal.

$ flutter pub get
$ flutter pub pub run flutter_launcher_icons:main

File list

These are file list after command execution.

+1 -1 M android/app/src/main/AndroidManifest.xml
+0 -0 M android/app/src/main/res/mipmap-hdpi/ic_launcher.png
+0 -0 M android/app/src/main/res/mipmap-mdpi/ic_launcher.png
+0 -0 M android/app/src/main/res/mipmap-xhdpi/ic_launcher.png
+0 -0 M android/app/src/main/res/mipmap-xxhdpi/ic_launcher.png
+0 -0 M android/app/src/main/res/mipmap-xxxhdpi/ic_launcher.png
+0 -0 A icon/ic_launcher.png
+71 -0 A ios/Podfile
+1 -1 M ios/Runner.xcodeproj/project.pbxproj
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-20x20@1x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-20x20@2x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-20x20@3x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-29x29@1x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-29x29@2x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-29x29@3x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-40x40@1x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-40x40@2x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-40x40@3x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-60x60@1x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-60x60@2x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-60x60@3x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-76x76@1x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-76x76@2x.png
+0 -0 A ios/Runner/Assets.xcassets/AppIcon.appiconset/AppIcon-83.5x83.5@2x.png
+56 -0 M pubspec.lock
+5 -0 M pubspec.yaml

Links

flutter_launcher_icons | Dart Package
https://pub.dartlang.org/packages/flutter_launcher_icons

How to change the application launcher icon on Flutter? - Stack Overflow
https://stackoverflow.com/questions/43928702/how-to-change-the-application-launcher-icon-on-flutter

How to fix the error that the header file of Flutter Plugin does not find on iOS build

Rui Kowase — Sun, 01 Apr 2018 14:44:03 +0000

How to fix

Open the header file by XCode.
Change from Project to Public of Target Membership at right column.

👇

You need to do this for all file if there are multiple header files.

Environment

Flutter 0.1.5
Dart 2.0.0-dev.28.0
iPhone X - 11.2

Error message

/Users/rkowase/StudioProjects/stopwatch/ios/Runner/GeneratedPluginRegistrant.m:6:9: fatal error: 'firebase_admob/FirebaseAdMobPlugin.h' file not found
#import <firebase_admob/FirebaseAdMobPlugin.h>
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Memo

If you add the Firebase Plugin, you need to add GoogleService-Info.plist by XCode as written in Add Firebase to your iOS Project | Firebase .

Links

FirebaseAdMobPlugin.h file not found when using firebase_admob Plugin for Flutter - Stack Overflow
https://stackoverflow.com/questions/49473823/firebaseadmobplugin-h-file-not-found-when-using-firebase-admob-plugin-for-flutte

objective c - Swift compiler error: "non-modular header inside framework module" - Stack Overflow
https://stackoverflow.com/questions/24103169/swift-compiler-error-non-modular-header-inside-framework-module/24317456#24317456

"Made Podfiles use symlinks to local pods" not working · Issue #15099 · flutter/flutter
https://github.com/flutter/flutter/issues/15099

PathProvider not found on iOS build - Google Groups
https://groups.google.com/forum/#!msg/flutter-dev/7QRk1RphLDE/5rLS4CciBwAJ

Firebase for Flutter
https://codelabs.developers.google.com/codelabs/flutter-firebase/#4

Add Firebase to your iOS Project | Firebase
https://firebase.google.com/docs/ios/setup

Auto translation bot for Slack using Zapier

Rui Kowase — Sun, 01 Apr 2018 13:59:44 +0000

I created an auto translation bot for Slack using Zapier.

How to use

Add the reaction specified Zapier to the comment you want to translate.

How it works

The slack bot post a translated comment into thread when the reaction specified by Zapier is added.

How to create this Zap

Overview

1. Add TRIGGER - Slack (New Reaction Added)

Set which reaction will be triggered.

Reaction: 2en (Specify any Emoji)
Channel: (Not specified)
User: (Not specified)

2. Add FILTER - Filter by Zapier (Only continue if...)

Add this filter if you want to trigger the specific channels. (This task is optional)

3. Add ACTION - Formatter by Zapier (Text)

Extract the ID of the reacted comment from the permalink to prevent multiple posting.

Transform: Extract Pattern
Values (Input): The Message Permalink of Step 1
Pattern: .*/(.*)(\?.*)?

4. Add SEARCH - Slack (Find Message)

Search the ID of the reacted comment to prevent multiple posting.

Search Query: in:#<MESSAGE_CHANNEL_NAME> from:2en <OUTPUT_OF_STEP3>
Sort By: (Not specified)
Sort Direction: (Not specified)

5. Add FILTER - Filter by Zapier (Only continue if...)

Filter the Permalink of Step 4 to prevent multiple posting.

6. Add ACTION - Translate by Zapier (Translate Text)

Translate the original comment into English.

Source Language: (Not specified)
Text: The Message Text of Step 1
Target Language: English

7. Add ACTION - Slack (Send Channel Message)

Post the translated comment.

Channel: Use a Custom Value
Custom Value for Channel ID: The Message Channel Name of Step 1
Message Text: <TRANSLATION_OF_STEP6> <PERMALINK_OF_STEP1> original comment (<OUTPUT_OF_STEP3>) (<SOURCE_LANGUAGE_OF_STEP6>)

Post into thread.

Thread: Use a Custom Value
Custom Value for Thread Timestamp: The Message Ts of Step 1

How to add a click event to any widget of Flutter

Rui Kowase — Sun, 01 Apr 2018 08:27:33 +0000

How to add a click event to any widget of Flutter.

TL;DR

Use GestureDetector widget

Sample code

GestureDetector(
  onTap: () {
    print("onTap called.");
  },
  child: Text("foo"),
),

Environment

Flutter 0.1.5
Dart 2.0.0-dev.28.0

Link

user interface - Flutter - Container onPressed? - Stack Overflow
https://stackoverflow.com/questions/43692923/flutter-container-onpressed

Useful Chrome Extension for Flutter

Rui Kowase — Sun, 01 Apr 2018 04:44:40 +0000

There is a useful chrome extension for Flutter.
Flutter developer - Chrome Web Store

How to use

Click See source code for Container class on API Doc.

https://docs.flutter.io/flutter/widgets/Container-class.html

You can jump the source code.

https://github.com/flutter/flutter/blob/master/packages/flutter/lib/src/widgets/container.dart#L232

Link

Flutter developer - Chrome Web Store
https://chrome.google.com/webstore/detail/flutter-developer/kimjiioacelfpeflakmeclmfndijcfpp

DEV Community: Rui Kowase

LeetCode in Kotlin: 20. Valid Parentheses

Problem

Solution

Test code

Model solution

Approach 1: Stacks

LeetCode in Kotlin: 7. Reverse Integer

Problem

Solution

Test code

Model solution

Approach 1: Pop and Push Digits & Check before Overflow

LeetCode in Kotlin: 1. Two Sum

Problem

Solution

Test code

Model solution

Approach 1: Brute Force

Approach 2: Two-pass Hash Table

Approach 3: One-pass Hash Table

[Android] How to mock final class with Mockito2

Issue

Solution

How to generate Flutter app icons for iOS and Android

TL;DR

Environment

How to create

1. Add flutter_launcher_icons Plugin

2. Prepare app icon

3. Create app icons

File list

Links

How to fix the error that the header file of Flutter Plugin does not find on iOS build

How to fix

Environment

Error message

Memo

Links

Auto translation bot for Slack using Zapier

How to use

How it works

How to create this Zap

Overview

1. Add TRIGGER - Slack (New Reaction Added)

2. Add FILTER - Filter by Zapier (Only continue if...)

3. Add ACTION - Formatter by Zapier (Text)

4. Add SEARCH - Slack (Find Message)

5. Add FILTER - Filter by Zapier (Only continue if...)

6. Add ACTION - Translate by Zapier (Translate Text)

7. Add ACTION - Slack (Send Channel Message)

How to add a click event to any widget of Flutter

TL;DR

Sample code

Environment

Link

Useful Chrome Extension for Flutter

How to use

Link

1. Add `flutter_launcher_icons` Plugin