[LeetCode] 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].

寻找两数之和，利用map存储数组的值与索引，然后遍历数组找出map中的元素，返回元素的索引。需要注意的是返回的结果索引不能相等。

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int, int> m;
        for (int i = 0; i != nums.size(); i++)
            m[nums[i]] = i;
        for (int i = 0; i != nums.size(); i++) {
            int diff = target - nums[i];
            if (m.count(diff) && m[diff] != i)
                return {i, m[diff]};
        }
    }
};
// 6 ms