Leetcode Two sum problem

1. Two Sum

Working:

• seen keeps track of numbers we’ve already visited and their indices.
• For each num, we calculate complement = target-num.
• If the complement is already in seen, we return the pair of indices.
• Otherwise, we store the current number with its index.

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167. Two Sum II - Input Array Is Sorted

Working:

• Start with two pointers left at the beginning, right at the end.
• Compute the sum of the two numbers.
• If the sum equals the target, return their indices. - If the sum is too small, move left forward to increase the sum.
• If the sum is too large, move right backward to decrease the sum.