【代码随想录算法训练营——Day31】贪心算法——56.合并区间、738.单调递增的数字、968.监控二叉树

天选之女wow2025-10-09 16:03

LeetCode题目链接

https://leetcode.cn/problems/merge-intervals/

https://leetcode.cn/problems/monotone-increasing-digits/

https://leetcode.cn/problems/binary-tree-cameras/

题解

56.合并区间

自己写出来了，好棒。需要注意神奇的语句end = max(end, intervals[i][1]);。

738.单调递增的数字

这题注意int和string类型转换的方法，转成数字9的做法。

968.监控二叉树

难题，下周目写。

代码

cpp 复制代码

//56.合并区间
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

class Solution {
private:
    static bool cmp(const vector<int> a, const vector<int> b) {
        if (a[0] == b[0]) return a[1] < b[1];
        return a[0] < b[0];
    }
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        vector<vector<int>>result;
        if (intervals.size() == 0) return result;
        sort(intervals.begin(), intervals.end(), cmp);
        int end = intervals[0][1], start = intervals[0][0];
        for (int i = 1;i < intervals.size();i++) {
            if (end < intervals[i][0]) {
                result.push_back({ start, end });
				start = intervals[i][0];
				end = intervals[i][1];
            }
            else {
                end = max(end, intervals[i][1]);
            }
        }
        result.push_back({ start, end });
        return result;
    }
};

int main() {
    vector<vector<int>> nums1 = { {1,3} ,{2,6},{8,10},{15,18} }, nums2 = { {1,4} ,{4,5} }, nums3 = { {4,7} ,{1,4} }, nums4 = { {1,4} ,{2,3} };
	Solution s;
    vector<vector<int>> result = s.merge(nums4);
    for (int i = 0;i < result.size();i++) {
        for (int j = 0;j < result[i].size();j++) {
            printf("%d ", result[i][j]);
        }
        printf("\n");
    }
    return 0;
}

cpp 复制代码

//738.单调递增的数字