人人网 2014校园招聘笔试题

技术笔试题（一）

#include <iostream>

using namespace std;

int hash_table[100];

bool judge(int *a, int len, int x)
{
	memset(hash_table, 0, sizeof(hash_table));
	for (int i=0; i<len; ++i)
	{
		hash_table[x - a[i]] = 1;
	}

	for (int i=0; i<len; ++i)
	{
		if (hash_table[i] == 1)
		{
			return true;
		}
	}

	return false;
}

int main()
{
	int len = 10;
	int a[10] = {1, 3, 5, 7, 9, 4, 2, 8, 10, 6};
	int x = 19;

	if (judge(a, len, x))
	{
		cout<<"Yes"<<endl;
	}
	else
	{
		cout<<"No"<<endl;
	}
	system("pause");
	return 0;
}

本题解决方法：hash table。

时间复杂度：O(N)

空间复杂度：O(N)

#include <iostream>

using namespace std;

int find(int *a, int n)
{
	int t = a[0];
	int count = 0;
	for (int i=0; i<n; ++i)
	{
		if (count == 0)
		{
			t = a[i];
			count = 1;
			continue;
		}
		else
		{
			if (a[i] == t)
			{
				count++;
			}
			else
			{
				count--;
			}
		}
	}

	return t;
}

int main()
{
	int n = 10;
	int a[10] = {1, 3, 2, 3, 3, 4, 3, 3, 3, 6};

	cout<<find(a, n)<<endl;

	system("pause");
	return 0;
}

Time Complexity: O(n)

Space Complexity:O(1)