leetcode - 287. 寻找重复数

题目

代码

#include <iostream>
#include <vector>
#include <set>
using namespace std;

// 借助set集合 
int findDuplicate1(vector<int>& nums) {
    
	int n = nums.size();
	set<int> visited;
	int num;
	for(int i = 0; i < n; i++){
    
		if(!visited.count(nums[i])){
    
			visited.insert(nums[i]);
		}else{
    
			num =  nums[i];
		}
	}
	return num;
}

// 快慢指针判圈 
int findDuplicate(vector<int>& nums) {
    
	int slow = 0, fast = 0;
	do{
    
		slow = nums[slow];
		fast = nums[nums[fast]];
	}while(slow != fast);
	slow = 0;
	while(slow != fast){
    
		slow = nums[slow];
		fast = nums[fast];
	}
	return slow;
}

int main(){
    
	int n, res;
	cin>>n;
	vector<int> nums(n);
	for(int i = 0; i < n; i++){
    
		cin>>nums[i];
	}
	res = findDuplicate(nums);
	cout<<res;
    return 0;
}