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  • 0287. Find the Duplicate Number (M)

    Find the Duplicate Number (M)

    题目

    Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.

    Example 1:

    Input: [1,3,4,2,2]
    Output: 2
    

    Example 2:

    Input: [3,1,3,4,2]
    Output: 3
    

    Note:

    1. You must not modify the array (assume the array is read only).
    2. You must use only constant, O(1) extra space.
    3. Your runtime complexity should be less than O((n^2)).
    4. There is only one duplicate number in the array, but it could be repeated more than once.

    题意

    思路

    链表循环查找:参考 官方解答

    二分查找:参考 [LeetCode] 287. Find the Duplicate Number 寻找重复数


    代码实现

    Java

    链表循环

    class Solution {
        public int findDuplicate(int[] nums) {
            int slow = nums[0], fast = nums[0];
            do {
                slow = nums[slow];
                fast = nums[nums[fast]];
            } while (slow != fast);
            fast = nums[0];
            while (fast != slow) {
                slow = nums[slow];
                fast = nums[fast];
            }
            return slow;
        }
    }
    

    二分查找

    class Solution {
        public int findDuplicate(int[] nums) {
            int left = 1, right = nums.length - 1;
            while (left < right) {
                int mid = (right - left) / 2 + left;
                int count = 0;
                for (int num : nums) {
                    if (num <= mid) {
                        count++;
                    }
                }
                if (count <= mid) {
                    left = mid + 1;
                } else {
                    right = mid;
                }
            }
            return left;
        }
    }
    
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  • 原文地址:https://www.cnblogs.com/mapoos/p/13191049.html
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