解题报告 『HISTOGRA - Largest Rectangle in a Histogram（单调栈）』

原题地址

单调栈板子题，代码很简单。

注意将a[n + 1]赋值为0，防止栈中矩形未弹完。

 

代码实现如下：

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, a, b) for (register int i = (a); i <= (b); i++)

const int maxn = 1e5 + 5;

int n;
int a[maxn], sta[maxn], wid[maxn];

void origin() {memset(sta, 0, sizeof(sta));}

int MAX(int a, int b) {return a > b ? a : b;}

int read() {
    int x = 0, flag = 0;
    char ch = ' ';
    while (ch != '-' && (ch < '0' || ch > '9')) ch = getchar();
    if (ch == '-') {
        flag = 1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
        x = (x << 1) + (x << 3) + (ch ^ '0');
        ch = getchar();
    }
    return flag ? -x : x;
}

void write(int x) {
    if (x < 0) {
        putchar('-');
        x = -x;
    }
    if (x > 9) write(x / 10);
    putchar(x % 10 + '0');
}

signed main() {
    while (scanf("%d", &n) && n) {
        origin();
        rep(i, 1, n) a[i] = read();
        int ans = 0, p = a[n + 1] = 0;
        rep(i, 1, n + 1) {
            if (a[i] > sta[p]) {
                sta[++p] = a[i];
                wid[p] =1;
            }
            else {
                int width = 0;
                while (a[i] < sta[p]) {
                    width += wid[p];
                    ans = MAX(ans, 1ll * width * sta[p]);
                    p--;
                }
                sta[++p] = a[i];
                wid[p] = width + 1;
            }
        }
        write(ans);
        printf("\n");
    }
    return 0;
}