POJ 2082 Terrible Sets(单调栈)

#include <stdio.h>
#include <string.h>
#include <math.h>
#include <algorithm>
using namespace std;
typedef long long ll;
const int MAX_N = 50010;

int n;
ll height[MAX_N], width[MAX_N], sum[MAX_N];
int L[MAX_N], R[MAX_N], sta[MAX_N];

//维护单调非递减栈
int main()
{
while (~scanf("%d", &n)) {
if(n == -1) break;
sum[0] = 0;
for (int i = 1; i <= n; ++i) {
scanf("%lld%lld", &width[i], &height[i]);
sum[i] = sum[i - 1] + width[i];
}
height[n + 1] = 0, sum[n + 1] = sum
;
int top = 0, cur;
sta[0] = 0;
for (int i = 1; i <= n + 1; ++i) {
while(1) {
cur = sta[top];
if (height[cur] <= height[i]) break;
R[cur] = i;
top--;
}
L[i] = cur;
sta[++top] = i;
}
ll ans = 0;
for (int i = 1; i <= n; ++i) {
ll len = sum[R[i] - 1] - sum[L[i]];
//printf("L[%d] = %d R[%d] - 1 = %d\n", i, L[i], i, R[i] - 1);
ans = max(ans, len * height[i]);
}
printf("%lld\n", ans);
}
return 0;
}