两数之和

借助map辅助：

class Solution {
public:
    /**
     *
     * @param numbers int整型vector
     * @param target int整型
     * @return int整型vector
     */
    vector twoSum(vector &numbers, int target) {
        // write code here
        unordered_map m;
        // 1. 存储下标到map
        for (int i = 0; i < numbers.size(); ++i) m[numbers[i]] = i + 1;
        // 2. 再次扫描序列
        for (int i = 0; i < numbers.size(); ++i) {
            if (m.find(target - numbers[i]) != m.end()) {
                int idx = m[target - numbers[i]];
                vector vec = {i + 1, idx};
                if (idx > i + 1) return vec;
            }
        }
    }
};