[Amazon] Two Strings Are Anagrams (Compare Strings)

Write a method anagram(s,t) to decide if two strings are anagrams or not.

What is Anagram?
- Two strings are anagram if they can be the same after change the order of characters.

Example

Given s = "abcd", t = "dcab", return true.
Given s = "ab", t = "ab", return true.
Given s = "ab", t = "ac", return false.

Challenge 

O(n) time, O(1) extra space

思路：两串字符串分别统计每个出现字符的个数，如果有个数不等的，就不是anagram，反之

public class Solution {    /**     * @param s: The first string     * @param b: The second string     * @return true or false     */    public boolean anagram(String s, String t) {        Map<Character,Integer> mapS=new HashMap<>();        Map<Character,Integer> mapT=new HashMap<>();                for(int i=0;i<s.length();i++){            char ch=s.charAt(i);            if(!mapS.containsKey(ch)){                mapS.put(ch,1);            }else{                mapS.put(ch,mapS.get(ch)+1);            }        }        for(int i=0;i<t.length();i++){            char ch=t.charAt(i);            if(!mapT.containsKey(ch)){                mapT.put(ch,1);            }else{                mapT.put(ch,mapT.get(ch)+1);            }        }                for(int i=0;i<s.length();i++){            char ch=t.charAt(i);            if(mapS.get(ch)!=mapT.get(ch)){                return false;            }        }                return true;    }}

方法二：统计一个字符串里每个字符出现的个数，在统计另一个字符串字符的时候，个数- -，如果哪个字符的的总数不为0就false，反之。

public class Solution {    /**     * @param s: The first string     * @param b: The second string     * @return true or false     */    public boolean anagram(String s, String t) {        if(s.length()!=t.length()){            return false;        }                int[] count=new int[256];        for(int i=0;i<s.length();i++){            count[s.charAt(i)]++;        }        for(int i=0;i<t.length();i++){            count[t.charAt(i)]--;        }                for(int i=0;i<count.length;i++){            if(count[i]!=0){                return false;            }        }        return true;    }}

思路代码一样的55. Compare Strings :点击打开链接

public class Solution {    /**     * @param A : A string includes Upper Case letters     * @param B : A string includes Upper Case letter     * @return :  if string A contains all of the characters in B return true else return false     */    public boolean compareStrings(String A, String B) {        int[] count=new int[26];               for(int i=0;i<A.length();i++){            count[A.charAt(i)-'A']++;        }                for(int i=0;i<B.length();i++){            count[B.charAt(i)-'A']--;        }                for(int i=0;i<count.length;i++){            if(count[i]<0){                return false;            }        }        return true;    }}