A兩個相同字元之間的最長子字串

模擬 列舉

 1 class Solution {
 2 public:
 3     int maxLengthBetweenEqualCharacters(string s) {
 4         int n = s.size();
 5         int ans = -1;
 6         for (int i = 0; i < n; i++) {
 7             for (int j = i + 1; j < n; j++) {
 8                 if (s[i] == s[j]) {
 9
 
                     ans = max(ans, j - i - 1);
10                 }
11             }
12         }
13         return ans;
14     }
15 };

B執行操作後字典序最小的字串

DFS + 剪枝

 1 class Solution {
 2 public:
 3     string ans;
 4     map<string, int> m;
 5     void dfs(string s, int a, int b) {
 6
 
         if (m[s]) return ;
 7         m[s] = 1;
 8         ans = min(ans, s);
 9         string str = s;
10         for (int i = 1; i < str.size(); i += 2) {
11             int x = (str[i] - '0' + a) % 10;
12             str[i] = (x + '0');
13         }
14         dfs(str, a, b);
15         str = s.substr(s.size() - b, b) + s.substr(0
 
, s.size() - b);
16         dfs(str, a, b);
17     }
18     string findLexSmallestString(string s, int a, int b) {
19         ans = s;
20         dfs(s, a, b);
21         return ans;
22     }
23 };

C無矛盾的最佳球隊

D帶閾值的圖連通性