LeetCode 266. Palindrome Permutation

原题链接在这里：https://leetcode.com/problems/palindrome-permutation/

题目：

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

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

题解：

看能否配对出现.

Time Complexity: O(n). Space: O(n).

AC Java:

 1 public class Solution {
 2     public boolean canPermutePalindrome(String s) {
 3         if(s == null || s.length() <= 1){
 4             return true;
 5         }
 6         HashSet<Character> hs = new HashSet<Character>();
 7         for(int i = 0; i<s.length(); i++){
 8             char c = s.charAt(i);
 9             if(!hs.contains(c)){
10                 hs.add(c);
11             }else{
12                 hs.remove(c);
13             }
14         }
15         return hs.size() == 0 || hs.size() == 1;
16     }
17 }

可以用bitMap

Time Complexity: O(n). Space: O(256).

 1 public class Solution {
 2     public boolean canPermutePalindrome(String s) {
 3         if(s == null || s.length() <= 1){
 4             return true;
 5         }
 6         int [] map = new int[256];
 7         for(int i = 0; i<s.length(); i++){
 8             map[s.charAt(i)]++;
 9         }
10         int count = 0;
11         for(int i = 0; i<256; i++){
12             if(count == 0 && map[i]%2 == 1){ //第一次出现frequency为奇数的char
13                 count++;
14             }else if(map[i] % 2 == 1){ //第二次出现frequency为奇数的char
15                 return false;
16             }
17         }
18         return true;
19     }
20 }

类似Longest Palindrome.

跟上Palindrome Permutation II.