Poj 2796 單調棧

標籤：style   blog   color   使用   os   strong   

關於單調棧的性質，和單調隊列基本相同，只不過單調棧只使用數組的尾部，　類似於棧。

Accepted Code:

 1 /************************************************************************* 2     > File Name: 2796.cpp 3     > Author: Stomach_ache 4     > Mail: [email protected] 5     > Created Time: 2014年07月21日 星期一 22時45分56秒 6     > Propose:  7  ************************************************************************/ 8 #include <cmath> 9 #include <string>10 #include <cstdio>11 #include <fstream>12 #include <cstring>13 #include <iostream>14 #include <algorithm>15 using namespace std;16 17 typedef long long LL;18 const int maxn = 100005;19 int n;20 // b[i] holds the smallest index where a[b[i]]...a[i] are not larger than a[i], and e[i] is similar, just extends to the right of a[i]21 int a[maxn], b[maxn], e[maxn], st[maxn];22 LL sum[maxn]; //prefix sum  23 24 int25 main(void) {26 #ifndef ONLINE_JUDGE27       freopen("in.txt", "r", stdin);28 #endif29       while (~scanf("%d", &n)) {30           for (int i = 1; i <= n; i++) scanf("%d", a+i);31         for (int i = 1; i <= n; i++) b[i] = e[i] = i;32         sum[0] = 0;33         for (int i = 1; i <= n; i++) {34             sum[i] = sum[i-1] + a[i];35         }36         // the top of no decreasing stack37         int top = 0;38         for (int i = 1; i <= n; i++) {39               if (!top || a[i] > a[st[top-1]]) {40                 // push an element to stack41                   st[top++] = i;42             } else {43                   while (top > 0 && a[st[top-1]] > a[i]) {44                       // update e[st[top-1]]45                       e[st[top-1]] = i - 1;46                     // update b[i]47                     b[i] = b[st[top-1]];48                     // pop the toppest element of stack 49                       top--;50                 }51                 if (!top || a[st[top-1]] != a[i]) {52                       // push53                       st[top++] = i;54                 } else if(a[st[top-1] == a[i]]) {55                       // update b[i]56                       b[i] = b[st[top-1]];57                 }58             }59         }60         // update e[i] of those elements that still in the stack 61         for (int i = 0; i < top; i++) e[st[i]] = n;62         // find the answer63         LL ans = -1, bb, ee;64         for (int i = 1; i <= n; i++) {65               if (ans < a[i] * (sum[e[i]]-sum[b[i]-1])) {66                   ans = a[i] * (sum[e[i]]-sum[b[i]-1]);67                 bb = b[i];68                 ee = e[i];69             }70         }71         printf("%lld\n%lld %lld\n", ans, bb, ee);72     }73 74     return 0;75 }