LeetCode#1.Two Sum

题目描述

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.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

题目解析

有两种解法：

1. 直接两层循环遍历；

2. 使用map，直接找另一个数对应的下标。

代码1

class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
for(int i=0;i<nums.size()-1;++i)
{
for(int j=i+1;j<nums.size();++j)
{
if(nums[i]+nums[j]==target)
{
return {i,j};
}
}

}
return {};
}
};

代码2

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