题解 | #左旋转字符串#

方法1：三次翻转

public class Solution {
    public String LeftRotateString(String str,int n) {
        if(str.length()==0 || n>=str.length()){
            return str;
        }
        char[] chars=str.toCharArray();
        reverse(chars,0,n-1);
        reverse(chars,n,chars.length-1);
        reverse(chars,0,chars.length-1);
        return new String(chars);
    }
    public void reverse(char[] chars,int i,int j){
        while(i<j){
            swap(chars,i++,j--);
        }
    }
    public void swap(char[] chars,int i,int j){
        char temp=chars[i];
        chars[i]=chars[j];
        chars[j]=temp;
    }
}

方法2：substring()

public class Solution {
    public String LeftRotateString(String str,int n){
        if(str==null || n>str.length()){
            return str;
        }
        return str.substring(n)+str.substring(0,n);
    }
}

方法3：遍历

public class Solution {
    public String LeftRotateString(String str,int n) {
        if(str==null || n>str.length()){
            return str;
        }
        char[] ch=str.toCharArray();
        StringBuffer sb=new StringBuffer();
        for(int i=n;i<str.length();i++){
            sb.append(ch[i]);
        }
        for(int i=0;i<n;i++){
            sb.append(ch[i]);
        }
        return sb.toString();
    }
}