Codeforces 442C

题目链接

C. Artem and Array
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

Artem has an array of n positive integers. Artem decided to play with it. The game consists of n moves. Each move goes like this. Artem chooses some element of the array and removes it. For that, he gets min(a, b) points, where a and b are numbers that were adjacent with the removed number. If the number doesn't have an adjacent number to the left or right, Artem doesn't get any points.

After the element is removed, the two parts of the array glue together resulting in the new array that Artem continues playing with. Borya wondered what maximum total number of points Artem can get as he plays this game.

Input

The first line contains a single integer n (1 ≤ n ≤ 5·105) — the number of elements in the array. The next line contains n integers ai (1 ≤ ai ≤ 106) — the values of the array elements.

Output

In a single line print a single integer — the maximum number of points Artem can get.

Sample test(s)
Input
5
3 1 5 2 6
Output
11
Input
5
1 2 3 4 5
Output
6
Input
5
1 100 101 100 1
Output
102

Accepted Code:
 1 /*************************************************************************
 2     > File Name: E.cpp
 3     > Author: Stomach_ache
 4     > Mail: sudaweitong@gmail.com
 5     > Created Time: 2014年06月23日 星期一 22时48分29秒
 6     > Propose: 
 7  ************************************************************************/
 8 
 9 #include <cmath>
10 #include <string>
11 #include <vector>
12 #include <cstdio>
13 #include <fstream>
14 #include <cstring>
15 #include <iostream>
16 #include <algorithm>
17 using namespace std;
18 
19 #define min(x, y) ((x) < (y) ? (x) : (y))
20 typedef long long LL;
21 int n, a[500005];
22 int b[500005];
23 
24 int
25 main(void) {
26       while (~scanf("%d", &n) && n) {
27           for (int i = 1; i <= n; i++) {
28               scanf("%d", a + i);
29         }
30           if (n <= 2) {
31               puts("0"); continue;
32         }
33         LL  ans = 0;
34         int cnt = 0;
35         for (int i = 1; i <= n; i++) {
36               b[cnt++] = a[i];
37               while (cnt > 2 && b[cnt-2] <= b[cnt-1] && b[cnt-2] <= b[cnt-3]) {
38                   ans += min(b[cnt-1], b[cnt-3]);
39                 b[cnt-2] = b[cnt-1];
40                 cnt--;
41             }
42         }    
43         for (int i = 1; i < cnt-1; i++) {
44               ans += min(b[i-1], b[i+1]);
45         }
46         printf("%I64d\n", ans);
47     }
48 
49     return 0;
50 }

 

 

posted on 2014-06-24 13:29  Stomach_ache  阅读(310)  评论(0编辑  收藏  举报

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