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:
- 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.
Same Algorithm with LC. 142
Time: O(N)
class Solution {
public int findDuplicate(int[] nums) {
if (nums == null || nums.length == 0) {
return -1;
}
int fast = nums[nums[0]];
int slow = nums[0];
while (fast != slow) {
fast = nums[nums[fast]];
slow = nums[slow];
}
int head = 0;
while (head != slow) {
head = nums[head];
slow = nums[slow];
}
return slow;
}
}