Ayoub Ali

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# Longest Common Prefix-Solution in Dart

## Question - Difficulty -Easy

Write a function to find the longest common prefix string amongst an array of strings.

If there is no common prefix, return an empty string "".

Example 1:

Input: Strings = ["flower","flow","flight"]
Output: "fl"

Example 2:

Input: Strings = ["dog","raceCar","car"]
Output: ""
Explanation: There is no common prefix among the input strings.

Constraints:

1 <= Strings.length <= 200
0 <= Strings[i].length <= 200
Strings[i] consists of only lowercase English letters.

## Theoretical Description

1. Iterate through the string one by one from S1 till SN.
2. Start comparing the 0th index, 1st index … ith index simultaneously for each string.
3. In case, any of the ith index characters doesn’t match, terminate the algorithm and return the LPS(1,i)
4. Else, continue and after scanning of N strings, the LCP(S1…SN) can be obtained.

## Reminder:-

Both solution are perfect but the thing with the first solution is it take too much time to execute. so it end up with Time Exceed Error.

### BUT

Second Solution works like a charm.

``````class A {
// Not Working - Horizontal Scan
String longestCommonPrefix(List<String> strs) {
// Checking if the list is empty
if (strs.length == 0 || strs.isEmpty || strs.length == '') return "";

// Storing the first index value in a variable
String prefix = strs[0];

// looping the whole length of list inside the list
// like how many strings are available
for (var i = 0; i < strs.length; i++) {
// storing the whole list in a variable
String c = strs[i];
if (c.length == 0 || prefix == "") return "";
// setting the first index starting point in subString 0 is first string
// AND  entire length of the remaining list
prefix = prefix.substring(0, min(prefix.length, c.length));
for (var j = 0; j < c.length && j < prefix.length; j++) {
if (c[j] != prefix[j]) {
prefix = prefix.substring(0, j);
break;
}
}
}
return prefix;
}
}

class B {
// Vertical scan -Working
String longestCommonPrefix(List<String> strs) {
if (strs.length == 0 || strs.isEmpty || strs.length == '') return "";

// looping through the length of list
for (int i = 0; i < strs[0].length; i++) {
// storing the value of first index and the other strings
String c = strs[0][i];

// looping again the entire length without index
for (int j = 1; j < strs.length; j++) {
// if the the length is same as  the length of the above loop
//OR indexes of the list is not same as above
if (i == strs[j].length || strs[j][i] != c)
// returning the first index and subString starting
// from first index and the remaining index
return strs[0].substring(0, i);
}
}
return strs[0];
}
}
``````

Runtime: 426 ms, faster than 100.00% of Dart online submissions for Longest Common Prefix.
Memory Usage: 141.9 MB, less than 100.00% of Dart online submissions for Longest Common Prefix.