双指针算法样例

模板

for (int i = 0, j = 0; i < n; i ++ )
{
    while (j < i && check(i, j)) j ++ ;
    // 具体问题的逻辑
}

例题1

#include<iostream>
#define int long long
using namespace std;
signed main()
{
	int n;
	cin >> n;
	for (int i = 1; i <= n / 2; i++)
	{
		int sum = i;
		int j = i;
		while (sum < n)
		{
			j++;
			sum += j;
		}
		if (sum == n)
			cout << i << ' ' << j<<endl;
	}
	return 0;
}

例题2

#include<iostream>
using namespace std;
int a[100005], b[110];
int main()
{
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		cin >> a[i];
	}
	int maxn = 0;
	for (int i = 1,j = 1; i <= n; i++)
	{
		b[a[i]]++;//不能放在上面的for循环中
		while (b[a[i]] > 1)
		{
			b[a[j]]--;
			j++;
		}
		maxn = max(maxn, i - j + 1);
	}
	cout << maxn;
	return 0;
}

例题3

#include<iostream>
using namespace std;
int a[100005], b[100005];
int main()
{
	int n, m;
	cin >> n >> m;
	for (int i = 1; i <= n; i++)
		cin >> a[i];
	for (int i = 1; i <= m; i++)
		cin >> b[i];
	for (int i = 1,j=1; i <= n; i++)
	{
		while (a[i] != b[j])
		{
			j++;
		}
		if (j > m)
		{
			cout << "No";
			return 0;
		}
	}
	cout << "Yes";
	return 0;
}