LeetCode --- 287. 寻找重复数

• LeetCode链接：287. 寻找重复数

解法1 - 循环链表

class Solution {
    public int findDuplicate(int[] nums) {
        int slow = 0;
        int fast = 0;
        while (true) {
            slow = nums[slow];
            fast = nums[nums[fast]];
            if (slow == fast) break;
        }
        int a = 0;
        int b = slow;
        while ( a != b) {
            a = nums[a];
            b = nums[b];
        }
        return a;
    }
}

解法2 - 二分查找

class Solution {
    public int findDuplicate(int[] nums) {
        int len = nums.length;
        int left = 1;
        int right = len - 1;
        while (left < right) {
            int mid = (left + right) >> 1;
            int cnt = 0;
            for (int num : nums) {
                if (num <= mid) {
                    cnt += 1;
                }
            }
            if (cnt > mid) {
                // 重复元素位于区间 [left, mid]
                right = mid;
            } else {
                // [mid + 1, right]
                left = mid + 1;
            }
        }
        return left;
    }
}