[Leetcode] Palindrome permutation I & II

Palindrome permutation

Given a string, determine if a permutation of the string could form a palindrome.

For example,
"code", False, "aab" True, "carerac" .

Hint:

1. Consider the palindromes of odd vs even length. What difference does you notice?
2. Count the frequency of each character.
3. If Each character occurs even number of times, then it must is a palindrome. How about character which occurs odd number of times

1 classSolution {2  Public:3     BOOLCanpermutepalindrome (strings) {4vector<int> cnt ( the,0);5          for(auto a:s) + +Cnt[a];6         BOOLFlag =false;7          for(Auto n:cnt)if(N &1) {8             if(!flag) flag =true;9             Else return false;Ten         } One         return true; A     } -};

Palindrome permutation II

Given A string s , return all the palindromic permutations (without duplicates) of it. Return an empty list if no palindromic permutation could is form.

For example:

Given s = "aabb" , return ["abba", "baab"] .

Given s = "abc" , return [] .

Hint:

1. If a palindromic permutation exists, we just need to generate the first half of the string.
2. To generate all distinct permutations of a (half of) strings, use a similar approach from:permutations II or Next permutat Ion.

Do not follow the prompts, direct use of DFS, do not know the character does not meet the requirements.

1 classSolution {2  Public:3     voidDFS (vector<string> &res, vector<int> &cnt,string&s,intLintr) {4         if(L >=r) {5 Res.push_back (s);6             return;7         }8          for(inti =0; I < cnt.size (); ++i)if(Cnt[i] >=2) {9Cnt[i]-=2;TenS[L] = S[r] =i; OneDFS (RES, CNT, S, L +1+ U-1); ACnt[i] + =2; -         } -     } thevector<string> Generatepalindromes (strings) { -vector<int> cnt ( the,0); -          for(auto a:s) + +Cnt[a]; -         BOOLFlag =false; +          for(inti =0; I < cnt.size (); ++i)if(Cnt[i] &1) { -             if(!flag) { +Flag =true; AS[s.length ()/2] =i; at}Else { -                 return {}; -             } -         } -vector<string>Res; -DFS (RES, CNT, S,0, S.length ()-1); in         returnRes; -     } to};

[Leetcode] Palindrome permutation I & II