[LeetCode] Two Sum

http://oj.leetcode.com/problems/two-sum/

这道题如果第二层循环用二分, 那么时间复杂度是O(nlogn), 而我的做法是哈希表unordered_map, 幸好LeetCode支持C++11.

class Solution {
public:
    vector<int> twoSum(vector<int> &numbers, int target) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
       unordered_map<int, int> m;
       for (unsigned int i = 0; i < numbers.size(); ++i) {
           m[numbers[i]] = i;
       }
       vector<int> re;
       for (unsigned int i = 0; i < numbers.size(); ++i) {
           unordered_map<int, int>::iterator index;
           if ((index = m.find(target - numbers[i])) != m.end()) {
               re.push_back(i + 1);
               re.push_back(index->second + 1);
               break;
           }
       }
       return re;
    }
};