左右旋转字符串/数组

题目描述

汇编语言中有一种移位指令叫做循环左移（ROL），现在有个简单的任务，就是用字符串模拟这个指令的运算结果。对于一个给定的字符序列S，请你把其循环左移K位后的序列输出。例如，字符序列S=”abcXYZdef”,要求输出循环左移3位后的结果，即“XYZdefabc”。是不是很简单？OK，搞定它！

 

// 右旋转，先整体reverse，然后0到n，然后n到结尾

public void rotateRight(int[] num, int n) {
    if (num == null || num.length == 0 || n < 0) {
        return;
    }
    reverse(num, 0, num.length - 1);
    reverse(num, 0, n - 1);
    reverse(num, n, num.length - 1);
}

private void reverse(int[] num, int low, int high) {
    while (low < high) {
        int temp = num[low];
        num[low] = num[high];
        num[high] = temp;
        low++;
        high--;
    }
}

// 左旋转，和右旋转逻辑一致，左旋转n即右旋转length-n，

public void rotateLeft(int[] num, int n) {
    if (num == null || num.length == 0 || n < 0) {
        return;
    }
    int rotate = num.length - n;
    reverse(num, 0, num.length - 1);
    reverse(num, 0, rotate - 1);
    reverse(num, rotate, num.length - 1);
}

private void reverse(int[] num, int low, int high) {
    while (low < high) {
        int temp = num[low];
        num[low] = num[high];
        num[high] = temp;
        low++;
        high--;
    }
}