SDTBU2021暑假集训II B题（单调栈）

题目链接

//2021-07-29 15:40:21
#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;

const int N = 1e5+10;

int n;
int a[N], b[N];
int sta[N];

int main() {
    cin >> n;
    for(int i = 1; i <= n; i++) {
        scanf("%d", &a[i]);
    }
    int head = 0;
    sta[++head] = n;
    b[n] = 0;
    for(int i = n-1; i >= 1; i--) {
        while(head && a[i] > a[sta[head]]) {
            b[i]++;
            b[i] += b[sta[head]];
            head--;
        }
        sta[++head] = i;
    }
    long long sum = 0;

    for(int i = 1; i <= n; i++) {
        //printf("%d**\n", b[i]);
        sum += b[i];
    }
    printf("%lld\n", sum);
    

    return 0;
}