代码随想录算法训练营第37天|738.单调递增的数字 、 714. 买卖股票的最佳时机含手续费、 968.监控二叉树

 738.单调递增的数字

题目链接

738. 单调递增的数字

我的题解

class Solution {
public:
    int monotoneIncreasingDigits(int n) {
        string s = to_string(n);
        for (int i = s.size() - 2; i >= 0; i --) {
            if (s[i] > s[i + 1]) {
                s[i] --;
                for (int j = i + 1; j < s.size(); j ++) s[j] = '9';
            }
        }
        return stoi(s);
    }
};

714. 买卖股票的最佳时机含手续费

题目链接

714. 买卖股票的最佳时机含手续费

我的题解

class Solution {
public:
    int maxProfit(vector& prices, int fee) {
        int res = 0, min_price = prices[0];
        for (int i = 0; i < prices.size(); i ++) {
            min_price = min(min_price, prices[i]);
            if (prices[i] > min_price + fee) {
                res += prices[i] - min_price - fee;
                min_price = prices[i] - fee;
            }
        }
        return res;
    }
};

968.监控二叉树

题目链接

968. 监控二叉树

我的题解

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    //val = 0;未被监视
    //val = 1;被监视但没摄像机
    //val = 2;有摄像机
    int res = 0;
    void backTracking(TreeNode* root) {
        if (root == nullptr) return;
        backTracking(root->left);
        backTracking(root->right);
        if (root->left == nullptr && root->right == nullptr) return;
        if ((root->left && root->left->val == 0) || (root->right && root->right->val == 0)) {
            if (root->left) root->left->val = 1;
            if (root->right) root->right->val = 1;
            root->val = 2;
            res ++;
            return;
        }
        if ((root->left && root->left->val == 2) || (root->right && root->right->val == 2)) {
            root->val = 1;
        }
        return;
    }
public:
    int minCameraCover(TreeNode* root) {
        TreeNode * node = new TreeNode;
        node->left = root;
        backTracking(node);
        return res;
    }
};