贪心+线程安全单例

TheLegendMe2025-11-28 12:28

cpp 复制代码

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

前一个数字 > 当前数字，说明单调性被破坏，需要把前一个数字减 1，并把它后面的所有数字变为 '9'

贪心算法：763.划分字母区间

cpp 复制代码

class Solution {
public:
    vector<int> partitionLabels(string s) {
        int hash[26] = {0};
        vector<int>result;
        int left = 0;
        int right = 0;
        for(int i = 0 ; i < s.size(); i ++ ) {
            hash[s[i] - 'a'] = i;  
        }
        for(int i = 0; i < s.size() ; i++ ) {
            right = max(right, hash[s[i] - 'a']);
            if(i == right) {
                result.push_back(right - left + 1);
                left = i + 1;
            }
        }
        return result;
    }
};

用个hash表保存

贪心算法：56.合并区间

cpp 复制代码

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

先把第一个存入，再依次比较。

线程安全的单例

cpp 复制代码

class singleton {
    public:
    static singleton &getinstance() {
        static singleton instance;
        return instance;
    }
    singleton (const singleton &) = delete;
    singleton& operator= (const singleton&) = delete;
    private:
    singleton() {

    }
    ~singleton() {

    }
};

int main() {
    singleton& pinstance = singleton::getinstance();
}