贪心+线程安全单例

1. 贪心算法：738.单调递增的数字

   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'

2. 贪心算法：763.划分字母区间

   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

3. 贪心算法：56.合并区间

   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。

4. 线程安全的单例

   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();
   }