ReverseString

今天第一次刷leetcode的题啊，最简单的一题，就出现超时不通过╮(╯▽╰)╭

题目如下：

Write a function that takes a string as input and returns the string reversed.

Example:
Given s = "hello", return "olleh".

 

我写的代码是：（真的是最笨的方法╮(╯▽╰)╭）

public static String reverseString(String s) {
        char[] arrs = s.toCharArray();
        String result = "";
        for (int i = (arrs.length - 1); i >= 0; i--) {
            result = result + arrs[i];
        }
        return result;
}

提交以后，超时啊~~

public String reverseString(String s) {
        if(s == null) return null;
        if(s.equals("")) return s;
        char[] arrChar = s.toCharArray();
        for (int i = 0, j = arrChar.length-1; i <= j; i++, j--) {
            char temp = arrChar[i];
            arrChar[i] = arrChar[j];
            arrChar[j] = temp;
        }
        return new String(arrChar);
 }

看了别人的讨论，如下几种方法 Many acceptable answers

Cheating Method using StringBuilder

public class Solution {
    public String reverseString(String s) {
        return  new StringBuilder(s).reverse().toString();
    }
}

 Classic Method by swapping first and last

public class Solution {
    public String reverseString(String s) {
        char[] word = s.toCharArray();
        int i = 0;
        int j = s.length() - 1;
        while (i < j) {
            char temp = word[i];
            word[i] = word[j];
            word[j] = temp;
            i++;
            j--;
        }
        return new String(word);
    }
}

 Same as previous but using byte instead

public class Solution {
    public String reverseString(String s) {
        byte[] bytes = s.getBytes();
        int i = 0;
        int j = s.length() - 1;
        while (i < j) {
            byte temp = bytes[i];
            bytes[i] = bytes[j];
            bytes[j] = temp;
            i++;
            j--;
        }
        return new String(bytes);
    }
}

Classic Method by swapping first and last
If you don't like temp variable

public class Solution {
    public String reverseString(String s) {
        byte[] bytes = s.getBytes();
        int i = 0;
        int j = s.length() - 1;
        while (i < j) {
            bytes[i] = (byte)(bytes[i] ^ bytes[j]);
            bytes[j] = (byte)(bytes[i] ^ bytes[j]);
            bytes[i] = (byte)(bytes[i] ^ bytes[j]);
            i++;
            j--;
        }
        return new String(bytes);
    }
}

Using recursion

public class Solution {
    public String reverseString(String s) {
        int length = s.length();
        if (length <= 1) return s;
        String leftStr = s.substring(0, length / 2);
        String rightStr = s.substring(length / 2, length);
        return reverseString(rightStr) + reverseString(leftStr);
    }
}

 

脑子短路ing