LeetCode（1）Two Sum

【题目】

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9

Output: index1=1, index2=2

【答案】

一、暴力法：

int *twoSum(int *nums,int numsSize,int target){int startindex=0;int endindex=0;int find;int *answer;answer=(int *)malloc(sizeof(int)*2);for (int i=0;i<numsSize;i++){int res=target-nums[i];find=0;for (int j=i+1; j<numsSize;j++){if (nums[j]==res){startindex=(i<j)?i:j;endindex=i+j-startindex;find=1;break;}}if (find==1){answer[0]=startindex+1;answer[1]=endindex+1;return answer;}}return answer;}

二、哈希表

vector <int> HashtwoSum(vector<int> &nums,int target){unordered_map<int,int> m;int i;for ( i=0;i<nums.size();i++){m[nums[i]]=i;}unordered_map<int,int>::iterator it;vector <int> answer;for ( i=0;i<nums.size();i++){int temp=target-nums[i];it=m.find(temp);if (it!=m.end()){int index=(*it).second;if ( index>i ){answer.push_back(i+1);answer.push_back(index+1);return answer;}}}return answer;}