蓝桥杯小白入门赛第9场第4题 字典树考试

 738.单调递增的数字 

class Solution {
public:
    int monotoneIncreasingDigits(int n) {
        string a = to_string(n);
        int k = 0;
        for (int i = a.size() - 1; i > 0; i--) {
            if (a[i] < a[i - 1]) {
                k = i;
                a[i-1]--;
            }
        }
        cout << k << endl;
        if (k != 0){
            for (int i = a.size() - 1; i >= k; i--) {
                a[i] = '9';
            }
    }
    return stoi(a);
}
}
;

 968.监控二叉树 

class Solution {
public:
    int ans = 0;
    // 0是未被覆盖，1是摄像头位，2是被覆盖
    int dfs(TreeNode* node) {
        if (node==NULL)
            return 2;
        int left = dfs(node->left);
        int right = dfs(node->right);
        if (left == 0 || right == 0) {
            ans++;
            return 1;
        }
        if (left == 1 || right == 1) {
            return 2;
        }
        return 0;
    }
    int minCameraCover(TreeNode* root) {
        if (dfs(root) == 0)
            ans++;
        return ans;
    }
};