【LeetCode】字符串反转函数的几个算法 Reverse String

题目：

Write a function that takes a string as input and returns the string reversed.
Example:
Given s = "hello", return "olleh".

//反转字符串方法1.最容易想到

public String reverseString(String s) {    if(s == null)        return null;    int len = s.length();    char[] cTmp = s.toCharArray();    char[] cRes = new char[len];    for (int i = 0; i < len; i++) {        cRes[i] = cTmp[len-1-i];    }    String sRes = String.valueOf(cRes);    return sRes;}
方法2.省了个过渡的数组

public String reverseString1(String s) {    if(s == null)        return null;    int len = s.length();    char[] cTmp = s.toCharArray();    char c;    for (int i = 0; i < len>>1; i++) {        c = cTmp[i];        cTmp[i] = cTmp[len -1 - i];        cTmp[len -1 - i] = c;    }    String sRes = String.valueOf(cTmp);    return sRes;}
方法3. 方法2的另一种表现形式

public String reverseString2(String s){        if(s == null || s.length() == 0)            return "";        char[] cs = s.toCharArray();        int begin = 0, end = s.length() - 1;        while(begin <= end){            char c = cs[begin];            cs[begin] = cs[end];            cs[end] = c;            begin++;            end--;        }        return new String(cs);}方法4.使用现成的函数

public String reverseString3(String s){

    StringBuilder sb = new StringBuilder(s);    return sb.reverse().toString();//reverse源码中也是用reverseString1（）这种方法，法234基本相同。StringBuilder线程不安全}