写两个水题放松下心情了属于是

1. 两数之和

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

202. 快乐数

跟bfs搜索的去重（也是这样处理数字）有异曲同工之处

class Solution {
public:
    int f(int n)
    {
        int res = 0;
        while (n > 0)
        {
            res += (n % 10) * (n % 10);
            n /= 10;
        }
        return res;
    }

    bool isHappy(int n) {
        unordered_set<int> set;
        while (n != 1)
        {
            int tmp = f(n);
            if (set.find(tmp) != set.end())
                return false;
            set.insert(tmp);
            n = tmp;
        }
        return true;
    }
};

349. 两个数组的交集

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        unordered_set<int> set;
        for (auto i : nums1) set.insert(i);
        unordered_set<int> res;
        for (int i : nums2)
        {
            if (set.find(i) != set.end())
            {
                res.insert(i);
            }
        }
        return vector<int>{res.begin(), res.end()};
    }
};

242. 有效的字母异位词

class Solution {
public:
    bool isAnagram(string s, string t) {
        unordered_map<char, int> umap;
        for (auto i : s) umap[i] ++;
        for (auto i : t) umap[i] --;
        for (auto [x, y] : umap)
        {
            if (y != 0)
                return false;
        }
        return true;
    }
};