題目描述
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, 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].
解法
1.暴力法時間複雜度O(n2)
2.hash map+在線處理
class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
map<int,int> mapp;
for(int i=0;i<nums.size();i++){
int diff=target-nums[i];
if(mapp.find(diff)!=mapp.end()){
return vector<int>{mapp[diff],i};
}
else mapp[nums[i]]=i;
}
return vector<int>{-1,-1};
}
};