单调栈、单调队列

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单调栈

AcWing 830

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#include<bits/stdc++.h>
using namespace std;

const int N = 100010;

int n;
int stk[N], tt;

int main(int argc, char const *argv[])
{	
    //ios::sync_with-stdio(false),cin.tie(0),cout.tie(0);//也可
	scanf("%d", &n);//输入输出数据较大，使用C库函数
	
	for (int i = 0; i < n; i ++){
		int x;
		scanf("%d", &x);
		/*单调栈，找寻数字左边比它小的最近的数*/
		while (tt && stk[tt] >= x ) tt --; // 维护单调栈
		if (tt) printf("%d ", stk[tt]);
		else printf("-1 ");
	
		stk[ ++ tt] = x; // 补充单调栈
	}

	return 0;
}

单调队列

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/*单调队列，可求滑动窗口的**最大值、最小值**、二分找值，多重背包*/

#include<bits/stdc++.h>

using namespace std;

const int N = 100010;

int n, k;
int a[N], q[N];

int main(int argc, char const *argv[])
{	
	scanf("%d", &n);//输入输出数据较大，使用C库函数
	//ios::sync_with-stdio(false),cin.tie(0),cout.tie(0);

	for (int i = 0; i < n; i ++) scanf("%d", &a[i]);
	
	/* 最小值 */
	int hh = 0, tt = -1;
	for (int i = 0; i < n; i ++){
		//判断队头是否已经滑出窗口
		if (hh <= tt && i - k + 1 > q[hh]) hh ++ ;
		while(hh <= tt && a[q[tt]] >= a[i]) tt -- ;
		q[ ++ tt] = i;
		if(i >= k - 1) printf("%d ", a[q[hh]]);
	}

	puts("");

	/* 最大值 */
	int hh = 0, tt = -1;
	for (int i = 0; i < n; i ++){
		//判断队头是否已经滑出窗口
		if (hh <= tt && i - k + 1 > q[hh]) hh ++ ;
		while(hh <= tt && a[q[tt]] <= a[i]) tt -- ;
		q[ ++ tt] = i;
		if(i >= k - 1) printf("%d ", a[q[hh]]);
	}

	puts("");

	return 0;
}

洛谷P1886题解

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#include <bits/stdc++.h>

using namespace std;

const int N = 1000006;

int a[N];

deque<int>q;

int main(){
    int n, m; 	cin >> n >> m;
    for (int i = 1; i <= n; ++i)
    {
        cin >> a[i];
    }
    for (int i = 1; i <= n; ++i)
    {
        while(!q.empty() && a[q.back()] > a[i]) q.pop_back();
        q.push_back(i);
        if (i >= m){
        	q.push_back(i);
            while (!q.empty() && q.front() <= i - m)    q.pop_front();
            printf("%d ", a[q.front()]);
        }
    }
    printf("\n");
    while (!q.empty()) q.pop_front();
    for (int i = 1; i <= n; ++i)
    {
        while(!q.empty() && a[q.back()] < a[i]) q.pop_back();
        q.push_back(i);
        if (i >= m){
        	q.push_back(i);
            while (!q.empty() && q.front() <= i - m)    q.pop_front();
            printf("%d ", a[q.front()]);
        }
    }
    //printf("\n");
    return 0;
}

HDU 1003

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#include <bits/stdc++.h>

using namespace std;

const int INF = 0x7fffffff;

int main(){
    int t; cin >> t;
    for (int i = 1; i <= t; ++i)
    {
    	int n; cin >> n;
    	int maxsum = -INF;
    	int start = 1, end = 1, p = 1;
    	int sum = 0;
    	for (int j = 1; j <= n; ++j)
    	{
    		int a; cin >> a; sum += a;
    		if (sum > maxsum){maxsum = sum; start = p; end = j;}
    		if (sum < 0){
    			sum = 0;
    			p = j + 1;
    		}
    	}
    	printf("Case %d:\n", i);printf("%d %d %d\n", maxsum,start,end);
    	if(i != t)cout << endl;
    }
    return 0;
}