leetcode_1: two sum

暴力

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

两遍hash

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        map<int, int> m;
        vector<int> b(2, -1);
        for(int i = 0; i < nums.size(); ++i){
            m.insert(map<int, int>::value_type(nums[i], i));
        }
        for(int i = 0; i < nums.size(); ++i){
            if(m.count(target - nums[i]) > 0 && m[target - nums[i]] != i){
                b[0] = i;
                b[1] = m[target - nums[i]];
                break;
            }
        }
        return b;
    }
};

一遍hash

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        map<int, int> m;
        vector<int> b(2, -1);

        for(int i = 0; i < nums.size(); ++i){
            if(m.count(target - nums[i]) > 0){
                b[0] = i;
                b[1] = m[target - nums[i]];
                break;
            }
            m[nums[i]] = i;
        }
        return b;
    }
};