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.
Note:
- You must not modify the array (assume the array is read only).
- You must use only constant, O(1) extra space.
- Your runtime complexity should be less than O(n2).
- There is only one duplicate number in the array, but it could be repeated more than once.
一刷
题解：由于数组长度为n+1，且数组中的元素的大小在[1, n]
思路同142， 快慢指针。
duplicate: entry of the circle
meet place: circle
class Solution {
public int findDuplicate(int[] nums) {
if(nums.length<1) return -1;
int slow = nums[0];
int fast = nums[nums[0]];
while(slow!=fast){
slow = nums[slow];
fast = nums[nums[fast]];
}
fast = 0;
while(fast!=slow){
fast = nums[fast];
slow = nums[slow];
}
return fast;
}
}
