19.1.11 LeetCode 1. 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].

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        map<int, int>hash;
        for (int i = 0; i < nums.size(); i++)
        {
            hash[target - nums[i]] = nums[i];
            if (hash.find(nums[i])!=hash.end()) {
                for (int j = 0; j < i; j++)
                    if (nums[i] + nums[j] == target)
                        return vector<int>{j, i};
            }
        }
    }
};

是哈希表啊！

一开始想用排序二分，没有想到用哈希呢。