hash數組找重複元素

將arr元素值移動到arr對應的下標即可： 

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

class Solution {
public:
	vector<int> findDuplicates(vector<int>& nums) {
		vector<int> res;
		for (int i = 0; i < nums.size(); i++) {
			while (nums[nums[i] - 1] != nums[i]) {
				swap(nums[nums[i] - 1], nums[i]);

			}
		}

		for (int i = 0; i < nums.size(); i++) {
			if (nums[i] != i + 1) res.push_back(nums[i]);
		}

		return res;
	}
};
int main() {
	vector<int> input = { 4,3,2,7,8,2,3,1 };
	Solution* ptr = new Solution();
	vector<int> res = ptr->findDuplicates(input);
	for (int i = 0; i < res.size(); ++i) {
		cout << res[i] <<' ';
	}
	for (;;);
}