Valid Anagram 解答

Question

Given two strings s and t, write a function to determine if t is an anagram of s.

For example,
s = "anagram", t = "nagaram", return true.
s = "rat", t = "car", return false.

(An anagram is a type of word play, the result of rearranging the letters of a word or phrase to produce a new word or phrase, using all the original letters exactly once; for example Torchwood can be rearranged into Doctor Who.)

Solution

Use hashmap to count each character's appearance time. Time complexity O(n), space cost O(n).

Note here, counts.put(tmp, count.get(tmp)--); is wrong!

 public class Solution {
     public boolean isAnagram(String s, String t) {
         if (s == null || t == null)
             return false;
         if (s.length() != t.length())
             return false;
         Map<Character, Integer> counts = new HashMap<Character, Integer>();
         int length = s.length();
         for (int i = 0; i < length; i++) {
             char tmp = s.charAt(i);
             if (counts.containsKey(tmp)) {
                 int count = (int)counts.get(tmp);
                 counts.put(tmp, count + 1);
             } else {
                 counts.put(tmp, 1);
             }
         }
         for (int i = 0; i < length; i++) {
             char tmp = t.charAt(i);
             if (counts.containsKey(tmp)) {
                 int count = (int)counts.get(tmp);
                 if (count <= 0)
                     return false;
                 else
                     counts.put(tmp, count - 1);
             } else {
                 return false;
             }
         }
         return true;
     }
 }

++x is called preincrement while x++ is called postincrement.

 int x = 5, y = 5;

 System.out.println(++x); // outputs 6
 System.out.println(x); // outputs 6

 System.out.println(y++); // outputs 5
 System.out.println(y); // outputs 6