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leetcode.com/problems/two-sum

1. Two Sum Easy

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

JavaSolution.java

class Solution {
  public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> seen = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
      int need = target - nums[i];
      // TODO: check seen?
      seen.put(nums[i], i);
    }
    return new int[0];
  }
}

AlgoSolveo TutorSocratic

What happens if you store each number you've seen in a HashMap?

Then I can check if target − num is already there!

Exactly. What's the time complexity now?

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