左旋转字符串

左旋转字符串

public String LeftRotateString(String str,int n) {
    if(str==null || str.length()==0){
        return "";
    }
    char[] chs = str.toCharArray();
    if(n>chs.length){
        return str;
    }
    reverse(chs,0,chs.length-1);
    reverse(chs,0,chs.length-n-1);
    reverse(chs,chs.length-n,chs.length-1);
    return new String(chs);
}

//将[start,end] 之间的字符串反转
private void reverse(char[] chs,int start,int end){
    while (start<end){
        char tmp = chs[start];
        chs[start] = chs[end];
        chs[end] = tmp;
        start++;
        end--;
    }
}

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