Leetcode 001 题
Difficulty:Easy
**Tag: Map **
题目
题目原址：https://leetcode.com/problems/two-sum/#/description
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.
例子
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
思路
其实就是一个边建立字典边访问字典的过程：
字典的key-value 分别为
key: nums[i]
value: index
伪代码更能描述这个过程
for num in nums
1. if target - num in dict
2. 说明字典中存在一个元素 + num = target，返回下标
3.将num放入dict中
代码
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
unordered_map<int, int> mm;
for(int i = 0; i < nums.size(); i++)
{
if(mm.count(target - nums[i]))
{
return {i, mm[target - nums[i]]};
}
mm[nums[i]] = i;
}
return {};
}
};