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

Day 37

738. 单调递增的数字

class Solution {
public:
    int monotoneIncreasingDigits(int n) {
        string strN = to_string(n);
        int i = 1;
        while (i < strN.length() && strN[i - 1] <= strN[i]) {
            i += 1;
        }
        if (i < strN.length()) {
            while (i > 0 && strN[i - 1] > strN[i]) {
                strN[i - 1] -= 1;
                i -= 1;
            }
            for (i += 1; i < strN.length(); ++i) {
                strN[i] = '9';
            }
        }
        return stoi(strN);
    }
};

714. 买卖股票的最佳时机含手续费

class Solution {
public:
    int maxProfit(vector& prices, int fee) {
        int n = prices.size();
        int buy = prices[0] + fee;
        int profit = 0;
        for (int i = 1; i < n; ++i) {
            if (prices[i] + fee < buy) {
                buy = prices[i] + fee;
            }
            else if (prices[i] > buy) {
                profit += prices[i] - buy;
                buy = prices[i];
            }
        }
        return profit;
    }
};

968. 监控二叉树

struct Status {
    int a, b, c;
};

class Solution {
public:
    Status dfs(TreeNode* root) {
        if (!root) {
            return {INT_MAX / 2, 0, 0};
        }
        auto [la, lb, lc] = dfs(root->left);
        auto [ra, rb, rc] = dfs(root->right);
        int a = lc + rc + 1;
        int b = min(a, min(la + rb, ra + lb));
        int c = min(a, lb + rb);
        return {a, b, c};
    }

    int minCameraCover(TreeNode* root) {
        auto [a, b, c] = dfs(root);
        return b;
    }
};