LeetCode 287. Find the Duplicate Number

分析

难度 中

来源

https://leetcode.com/problems/find-the-duplicate-number/

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(n²).
4. There is only one duplicate number in the array, but it could be repeated more than once.

解答

package LeetCode;

public class L287_FindTheDuplicateNumber {
    public int findDuplicate(int[] nums) {
        int slow=nums[0];
        int fast=nums[nums[0]];
        while(slow!=fast){
            slow=nums[slow];
            fast=nums[nums[fast]];
        }
        int slow2=0;
        while(slow2!=slow){
            slow=nums[slow];
            slow2=nums[slow2];
        }
        return slow;
    }
    public static void main(String[] args){
        L287_FindTheDuplicateNumber l287=new L287_FindTheDuplicateNumber();
        int[] nums={3,1,3,4,2};
        System.out.println(l287.findDuplicate(nums));
    }
}