Two Sum LeetCode Solution

Table of Contents

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

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

Example 1:

Input: nums = [2,7,11,15], target = 9 Output: [0,1] Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6 Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6 Output: [0,1]

Constraints:

2 <= nums.length <= 103
-109 <= nums[i] <= 109
-109 <= target <= 109
Only one valid answer exists.

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

Solution
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class Solution { public: vector twoSum(vector& a, int target) { unordered_map<int, int> m; // element and its index mapping vector res;

    m\[a\[0\]\] = 0; // first index
    
    for(int i=1; i<a.size(); i++) {
        int diff = target - a\[i\];
        
        if(m.find(diff) != m.end()) {
            res.push\_back(m\[diff\]);
            res.push\_back(i);
        }
        
        m\[a\[i\]\] = i;
    }
    
    return res;
}

};

Solution #

Solution
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