Two Sum —— Leetcode

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

用hashtable解决和为target的问题。

源码不太美观，还是搜一下leetcode上votes最高的答案吧。

class Solution {
public:
vector<int> twoSum(vector<int>& nums, int target) {
std::unordered_map<int, int> m;
vector<int> res;

for(int i=0; i<nums.size(); ++i) {
if(m[nums[i]] == 0)
m[nums[i]] = i+1;
}

int tmp = 0;
for(int j=0; j<nums.size(); ++j) {
tmp = m[target-nums[j]];
if(tmp > 0) {
if(tmp != j+1) {
res.push_back(min(tmp, j+1));
res.push_back(max(tmp,j+1));
break;
}
}
}

return res;
}
};