POJ 3250 Bad Hair Day 單調棧

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維護一個單調遞減的棧 每次家進棧首的牛必定可以被其他棧裡面的牛看到

#include <cstdio>#include <cstring>using namespace std;const int maxn = 80010;typedef unsigned long long LL;int a[maxn], s[maxn];int main(){int n;scanf("%d", &n);for(int i = 1; i <= n; i++)scanf("%d", &a[i]);int top = 0;LL ans = 0;for(int i = 1; i <= n; i++){while(top && a[i] >= a[s[top]])top--;ans += top;s[++top] = i;}printf("%llu\n", ans);return 0;}

POJ 3250 Bad Hair Day 單調棧