Leetcode:find the Duplicate number

Find the Duplicate number


Total Accepted: 29207 Total Submissions: 74613 Difficulty: Hard

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 are only one duplicate number, find the duplicate one.

Note:

1. You must the Modify the array (assume the array was read only).
2. You must use only constant, O(1) Extra space.
3. Your runtime complexity should is less than O(n2) .
4. There is a duplicate number in the array, but it could was repeated more than once.

Credits:
Special thanks to @jianchao. Li.fighter for adding the problem and creating all test cases.

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Hide TagsBinary Search Array of pointersHide Similar Problems(H) First Missing Positive (m) single number (m) Linked List Cycle II (m) Missing number

Ideas:

The solution is similar to the entry point in the linked list where the ring is found.

C + + code:

Class Solution {public:    int findduplicate (vector<int>& nums) {                int size = Nums.size ();                if (Size < 2) return-1;                int slow = nums[0];        int fast = Nums[nums[0]];                while (slow! = fast) {            slow = Nums[slow];            Fast = Nums[nums[fast]];        }                Fast = 0;                while (slow! = fast) {            slow = Nums[slow];            Fast = Nums[fast];        }        return slow;}    ;

Leetcode:find the Duplicate number