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:
O(n2).Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.
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思路：
解法类似于找有环的链表中的入口点。
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
原文：http://blog.csdn.net/itismelzp/article/details/51569023