翻转字符串

循环

class Solution {
    public void reverseString(char[] s) {
        for (int i = 0; i < s.length ; i++){
            if(i >= s.length - i - 1){
                break;
            }
            char temp = s[i];
            s[i] = s[s.length -i -1];
            s[s.length -i -1] = temp;
        }
    }
}

递归

class Solution {
    public void reverseString(char[] s) {
        helper(s, 0, s.length - 1);
    }

    private void helper(char[] s, int left, int right){
        if(left >= right){
           return;  
        }

        char temp = s[left];
        s[left++] = s[right];
        s[right--] = temp;
        helper(s, left, right);
    }
}