Leetcode-1.Two Sum

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] Explanation:
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 <= 104
-109 <= nums[i] <= 109
-109 <= target <= 109 only one valid answer exists.

class Solution {
public:
    vector twoSum(vector& nums, int target) {
	vector retnum;
	for(int i=0;i 
解法二：哈希法 
#include
#include
#include
using namespace std;
vector twosum(vector& nums,int target){
	unordered_map num2;
	for(int i=0;isecond,i};
		}
		num2[nums[i]]=i;
	}
	return {};
} 
int main(){
	vector nums={2,7,11,15} ;
	for(auto i:twosum(nums,9))
		cout<