[LeetCode]1. 两数之和

给定一个整数数组和一个目标值，找出数组中和为目标值的两个数。

你可以假设每个输入只对应一种答案，且同样的元素不能被重复利用。

C++

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector <int> res;
        for (int i = 0; i < nums.size() - 1; i++) {
            for (int j = i+1; j < nums.size(); j++) {
                if (nums[i] + nums[j] == target) {
                    res.push_back(i);
                    res.push_back(j);
                }
            }
        }
        return res;
    }
};

C++

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int, int> m;
        vector<int> res;
        for (int i = 0; i < nums.size(); i++)
            m[nums[i]] = i;
        for (int i = 0; i < nums.size(); i++) {
            int t = target - nums[i];
            if (m.count(t) && m[t] != i) {
                res.push_back(i);
                res.push_back(m[t]);
                break;
            }
        }
        return res;
    }
};

C

/**
* Note: The returned array must be malloced, assume caller calls free().
*/
int* twoSum(int* nums, int numsSize, int target) {
    static int res[2]; int i, j;
    for (i = 0; i < numsSize - 1; i++) {
        for (j = i+1; j < numsSize; j++) {
            if (nums[i] + nums[j] == target) {
                res[0] = i;
                res[1] = j;
                break;
            }
        }
    }
    return res;
}