Valid Anagram 解答

最新推荐文章于 2020-12-16 10:28:45 发布

转载最新推荐文章于 2020-12-16 10:28:45 发布 · 61 阅读

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原文链接：http://www.cnblogs.com/ireneyanglan/p/4809024.html

本文介绍了一种使用哈希映射来判断两个字符串是否互为字谜变换的方法。通过统计每个字符出现的次数，并验证这些计数是否匹配，可以在O(n)的时间复杂度内解决问题。

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!

 1 public class Solution {
 2     public boolean isAnagram(String s, String t) {
 3         if (s == null || t == null)
 4             return false;
 5         if (s.length() != t.length())
 6             return false;
 7         Map<Character, Integer> counts = new HashMap<Character, Integer>();
 8         int length = s.length();
 9         for (int i = 0; i < length; i++) {
10             char tmp = s.charAt(i);
11             if (counts.containsKey(tmp)) {
12                 int count = (int)counts.get(tmp);
13                 counts.put(tmp, count + 1);
14             } else {
15                 counts.put(tmp, 1);
16             }
17         }
18         for (int i = 0; i < length; i++) {
19             char tmp = t.charAt(i);
20             if (counts.containsKey(tmp)) {
21                 int count = (int)counts.get(tmp);
22                 if (count <= 0)
23                     return false;
24                 else
25                     counts.put(tmp, count - 1);
26             } else {
27                 return false;
28             }
29         }
30         return true;
31     }
32 }

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

1 int x = 5, y = 5;
2 
3 System.out.println(++x); // outputs 6
4 System.out.println(x); // outputs 6
5 
6 System.out.println(y++); // outputs 5
7 System.out.println(y); // outputs 6

转载于:https://www.cnblogs.com/ireneyanglan/p/4809024.html