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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
题意：给定一组数和另一个数，在这组数中找两个数，使它们的和等于给定的数
思路1： --> 错，因为题目要求返回下标。
1.排序
2.两个下标，一个指向头，一个指向尾
3.如果下标指向的两个元素相加大于给定的数，尾下标减一
如果小于，头下标加一
思路2： hash
1.用hash存储每个数的下标
2.数组,看hash[target-num[i]]是否存在
复杂度：时间O(n)， 空间O(n)
class Solution {
public:
vector<int> twoSum(vector<int> &num, int target){
map<int, int> m;
vector<int> result;
for(int i = 0; i < num.size(); i++) m[num[i]] = i;
for(int i = 0; i < num.size(); i++){
int j = m[target - num[i]];
if(j && j != i){
result.push_back(i + 1);
result.push_back(j + 1);
return result;
}
}
}
};Leetcode 线性表 Two Sum,布布扣,bubuko.com
原文：http://blog.csdn.net/zhengsenlie/article/details/25832697