【一次过】Lintcode 1266. Find the Difference

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Given two strings s and t which consist of only lowercase letters.

String t is generated by random shuffling string s and then add one more letter at a random position.

Find the letter that was added in t.

样例

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

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解题思路1：

直观的思路就是用map。

public class Solution {
    /**
     * @param s: a string
     * @param t: a string
     * @return: the letter that was added in t
     */
    public char findTheDifference(String s, String t) {
        // Write your code here
        Map<Character,Integer> map = new HashMap<>();
        for(int i=0 ; i<s.length() ; i++){
            if(map.get(s.charAt(i)) == null)
                map.put(s.charAt(i),1);
            else
                map.put(s.charAt(i),map.get(s.charAt(i)) + 1);
        }
        
        for(int i=0 ; i<t.length() ; i++){
            if(!map.containsKey(t.charAt(i)) || map.get(t.charAt(i))<=0)
                return t.charAt(i);
            else
                map.put(t.charAt(i),map.get(t.charAt(i)) - 1);
        }
        
        return 'a';
    }
}

解题思路2：

我们也可以使用位操作Bit Manipulation来做，利用异或的性质，相同位返回0，这样相同的字符都抵消了，剩下的就是后加的那个字符，参见代码如下：

public class Solution {
    /**
     * @param s: a string
     * @param t: a string
     * @return: the letter that was added in t
     */
    public char findTheDifference(String s, String t) {
        // Write your code here
        char res = 0;
        
        for(char c : s.toCharArray())
            res ^= c;
        for(char c : t.toCharArray())
            res ^= c;
            
        return res;
    }
}