LeetCode 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:

 public class Solution {
     public boolean canPermutePalindrome(String s) {
         if(s == null || s.length() <= 1){
             return true;
         }
         HashSet<Character> hs = new HashSet<Character>();
         for(int i = 0; i<s.length(); i++){
             char c = s.charAt(i);
             if(!hs.contains(c)){
                 hs.add(c);
             }else{
                 hs.remove(c);
             }
         }
         return hs.size() == 0 || hs.size() == 1;
     }
 }

可以用bitMap

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

 public class Solution {
     public boolean canPermutePalindrome(String s) {
         if(s == null || s.length() <= 1){
             return true;
         }
         int [] map = new int[256];
         for(int i = 0; i<s.length(); i++){
             map[s.charAt(i)]++;
         }
         int count = 0;
         for(int i = 0; i<256; i++){
             if(count == 0 && map[i]%2 == 1){ //第一次出现frequency为奇数的char
                 count++;
             }else if(map[i] % 2 == 1){ //第二次出现frequency为奇数的char
                 return false;
             }
         }
         return true;
     }
 }

类似Longest Palindrome.

跟上Palindrome Permutation II.