[LeetCode 404, 405][简单]左叶子之和/数字转换为十六进制数

404.左叶子之和
题目链接

static const auto io_speed_up =[](){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    return 0;
}();
class Solution {
public:
    int sumOfLeftLeaves(TreeNode* root) {
        if(!root)return 0;
        TreeNode *left = root -> left;
        if(left &&!(left->left)&&!(left->right))return left -> val + sumOfLeftLeaves(root->right) ;
        else return sumOfLeftLeaves(root->right) + sumOfLeftLeaves(left);
    }
};

405.数字转换为十六进制数
题目链接

static const auto io_speed_up =[](){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    return 0;
}();
class Solution {
public:
    string toHex(int num) {
        if(!num)return "0";
        string ans = "";
        unsigned int k = num;
        while(k){
            int p = k & 15;
            if(p<10)ans += to_string(p);
            else ans += ('a' + p - 10);
            k>>=4;
        }
        reverse(ans.begin(), ans.end());
        return ans;
    }
};