Leetcode每日一题

457. 环形数组是否存在循环

package leetode每日一题;

/**
 * @Classname 环形数组是否存在循环457
 * @Description TODO
 * @Date 2021/8/7 12:48
 * @Created by xjl
 */
public class 环形数组是否存在循环457 {
    public boolean circularArrayLoop(int[] nums) {
        int n = nums.length;
        for (int i = 0; i < n; i++) {
            if (nums[i] == 0) {
                continue;
            }
            int slow = i;
            int fast = advance(nums, i);
            // 判断非零且方向相同
            while (sameSign(nums[slow], nums[fast]) && sameSign(nums[slow], nums[advance(nums, fast)])) {
                if (slow == fast) {
                    //跳过一直在内循环的过程
                    if (slow != advance(nums, slow)) {
                        return true;
                    } else {
                        break;
                    }
                }
                //设置快慢指针
                slow = advance(nums, slow);
                fast = advance(nums, advance(nums, fast));
            }
            //表示每一次都访问过了需要将这个设置为0
            int index = i;
            while (sameSign(nums[index], nums[advance(nums, index)])) {
                int tmp = index;
                index = advance(nums, index);
                nums[tmp] = 0;
            }
        }
        return false;
    }

    /**
     * @description TODO 判断是否符号相同的
     * @param: num1
     * @param: num2
     * @date: 2021/8/7 13:10
     * @return: boolean
     * @author: xjl
     */
    private boolean sameSign(int num1, int num2) {
        return (num1 > 0 && num2 > 0) || (num1 < 0 && num2 < 0);
    }

    /**
     * @description TODO 判断要走几步
     * @param: cur
     * @param: nums
     * @date: 2021/8/7 13:02
     * @return: int
     * @author: xjl
     */
    private int advance(int[] nums, int cur) {
        int len = nums.length;
        //计算的是走几步
        cur += nums[cur];
        //可能是正数越界的
        cur %= len;
        //表示有可能是负数
        cur += len;
        cur %= len;
        return cur;
    }

}