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]
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 <= 104
-109 <= nums[i] <= 109
-109 <= target <= 109
Only one valid answer exists.

三种语言的版本:python3 C++ Golang

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        nums_hash = {}
        for k, v in enumerate(nums):
            if v in nums_hash:
                return [k, nums_hash[v]]
            else:
                nums_hash[target-v] = k
            
        

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        map<int, int> numsHash;
        vector<int> result;
        for(int i = 0; i < nums.size(); i++){
            auto iter = numsHash.find(nums[i]);
            if(iter == numsHash.end()){
                numsHash[target-nums[i]] = i;
            }else{
                result.push_back(i);
                result.push_back(numsHash[nums[i]]);
                break;
            }
        }
        return result;
    
    }
        
};

func twoSum(nums []int, target int) []int {
    numsHash := make(map[int]int)
    result := make([]int, 2)
    for k, v := range nums{
        index, exists := numsHash[v]
        if exists{
            result[0] = index
            result[1] = k
            break
        }else{
            numsHash[target-v] = k
        }
    }
    return result
    
}