代码随想录day31 贪心05

想进个大厂2026-02-01 9:50

56. 合并区间

cpp 复制代码

class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        vector<vector<int>> res;
        sort(intervals.begin(), intervals.end(),
             [](const vector<int>& a, const vector<int>& b) {
                 return a[0] < b[0];
             });

        vector<int> temp = intervals[0];
        for (int i = 1; i < intervals.size(); i++) {
            if (intervals[i][0] <= temp[1]) {
                temp[1] = max(intervals[i][1],temp[1]);
            } else {
                res.push_back({temp[0], temp[1]});
                temp = intervals[i];
            }
        }
        res.push_back(temp);
        return res;
    }
};

738. 单调递增的数字

cpp 复制代码

class Solution {
public:
    int monotoneIncreasingDigits(int N) {
        string strNum = to_string(N);

        int flag = strNum.size();
        for (int i = strNum.size() - 1; i > 0; i--) {
            if (strNum[i - 1] > strNum[i]) {
                flag = i;
                strNum[i - 1]--;
            }
        }
        for (int i = flag; i < strNum.size(); i++) {
            strNum[i] = '9';
        }
        return stoi(strNum);
    }
};

968. 监控二叉树

cpp 复制代码

class Solution {
private:
    int result;
    int traversal(TreeNode* cur) {
        if (cur == NULL)
            return 2;
        int left = traversal(cur->left);   // 左
        int right = traversal(cur->right); // 右
        if (left == 2 && right == 2)
            return 0;
        else if (left == 0 || right == 0) {
            result++;
            return 1;
        } else
            return 2;
    }

public:
    int minCameraCover(TreeNode* root) {
        result = 0;
        if (traversal(root) == 0) { // root 无覆盖
            result++;
        }
        return result;
    }
};