查找数组中重复数字的三种方法-优快云博客

本文介绍了三种查找数组中重复数字的方法：第一种使用冒泡排序后查找相邻重复元素；第二种利用STL库进行排序和查找；第三种算法优化，通过交换元素位置直接找出重复数字，无需额外空间。

Question:找出数组中重复的数字。在一个长度为n的数组汇总，所有的数字均在0-n-1范围内，数组中某些数字是重复的。找出重复数字。

//解法一
#include<iostream>
#include<vector>

using namespace std;
const int SIZE =7;

void sort(int a[],int size)
{
	for (size_t i = 0; i < size; i++)
	{
		for (size_t j = i + 1; j < size; j++)
		{
			int tmp;
			if (a[i] < a[j])
			{
				tmp = a[i];
				a[i] = a[j];
				a[j] = tmp;
			}
		}
	}
}

void findRepeatedNum(int a[],int size,vector<int>&b)
{
	for (size_t i = 0; i < size; i++)
	{
		if (a[i]==a[i+1])
		{
			b.push_back(a[i]);
		}
	}
}

int main()
{
	int array[SIZE] = {0};
	vector<int>repeatnum;
	cout << "input " << SIZE << " numbers " << endl;
	for (size_t i = 0; i < SIZE; i++)
	{
		cin >> array[i];
	}
	cout << "the input numbers are: " << endl;
	for (size_t i = 0; i < SIZE; i++)
	{
		cout << array[i]<<" " ;
	}
	cout << endl;
	sort(array, SIZE);
	findRepeatedNum(array, SIZE, repeatnum);
	cout << "the repeat numbers are: " << endl;
	for (int i = 0;i <repeatnum.size();i++)
	{
		cout << repeatnum[i]<<" ";
	}
	cout << endl;

	system("pause");
	return 0;
}

//解法二 STL
#include<iostream>
#include<vector>
#include<set>
#include<algorithm>

using namespace std;
#define SIZE 7


void findRepeatedNum(vector<int>a, set<int>&b)
{
	for (int i = 0; i < a.size()-1; i++)
	{
		if (a[i] == a[i + 1])
		{
			b.insert(a[i]);
		}
	}
}


int main()
{
	vector<int>array(SIZE);
	set<int>repeatnum;
	cout << "input numbers:" << endl;
	for (size_t i = 0; i < SIZE; i++)
	{
		cin >> array[i];
	}
	cout << "the input numbers are: " << endl;
	for (size_t i = 0; i < SIZE; i++)
	{
		cout << array[i] << " ";
	}
	cout << endl;
	sort(array.begin(),array.end());
	findRepeatedNum(array,repeatnum);
	cout << "the repeat numbers are: " << endl;
	for (auto i=repeatnum.begin();i!=repeatnum.end();i++)
	{
		cout <<*i<< " ";
	}
	cout << endl;

	system("pause");
	return 0;
}

//解法三，算法优化
#include<iostream>
#include<vector>

using namespace std;
const int SIZE=7;

bool findrepeatNum(int a[],int size,vector<int>&b)
{
	if (a == nullptr || size <= 0)
	{
		return false;
	}
	for (size_t i = 0; i <size ; i++)
	{
		if (a[i] < 0 || a[i] > size - 1)
			return false;
	}
	for (size_t i = 0; i < size; i++)
	{
		if (i != a[i])
		{
			if (a[i]==a[a[i]])
			{
				b.push_back(a[i]);
			}
			int tmp=a[i];
			a[i] = a[tmp];
			a[tmp] = tmp;
		}
		if (i == size)
			return true;
	}
	return false;

}


int main()
{
	int array[SIZE] = { 0 };
	vector<int>repeatnum;
	cout << "input " << SIZE << " numbers " << endl;
	for (size_t i = 0; i < SIZE; i++)
	{
		cin >> array[i];
	}
	cout << "the input numbers are: " << endl;
	for (size_t i = 0; i < SIZE; i++)
	{
		cout << array[i] << " ";
	}
	cout << endl;
	findrepeatNum(array, SIZE, repeatnum);
	cout << "the repeat numbers are: " << endl;
	for (int i = 0; i < repeatnum.size(); i++)
	{
		cout << repeatnum[i] << " ";
	}
	cout << endl;
	system("pause");
	return 0;
}