53 lines
1.6 KiB
C++
53 lines
1.6 KiB
C++
// Source : https://leetcode.com/problems/find-the-duplicate-number/
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// Author : Hao Chen, Calinescu Valentin
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// Date : 2015-10-19
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/***************************************************************************************
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*
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* Given an array nums containing n + 1 integers where each integer is between 1 and
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* n (inclusive), prove that at least one duplicate number must exist.
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* Assume that there is only one duplicate number, find the duplicate one.
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*
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* Note:
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* > You must not modify the array (assume the array is read only).
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* > You must use only constant, O(1) extra space.
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* > Your runtime complexity should be less than O(n2).
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* > There is only one duplicate number in the array, but it could be repeated more than
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* once.
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*
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* Credits:
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* Special thanks to @jianchao.li.fighter for adding this problem and creating all test
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* cases.
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*
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***************************************************************************************/
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class Solution {
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public:
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//
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// This problem can be transfromed to "Linked List Cycle" problem.
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// There are two pointers, one goes one step, another goes two steps.
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//
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// Refer to: https://en.wikipedia.org/wiki/Cycle_detection
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//
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int findDuplicate(vector<int>& nums) {
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int n = nums.size();
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int one = n;
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int two = n;
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do{
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one = nums[one-1];
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two = nums[nums[two-1]-1];
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} while(one != two);
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//find the start point of the cycle
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one = n;
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while(one != two){
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one = nums[one-1];
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two = nums[two-1];
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}
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return one;
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}
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};
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