time limit per test 1 second
memory limit per test 256 megabytes
input standard input
output standard output
Hideo Kojima has just quit his job at Konami. Now he is going to find a new place to work. Despite being such a well-known person, he still needs a CV to apply for a job.
During all his career Hideo has produced n games. Some of them were successful, some were not. Hideo wants to remove several of them (possibly zero) from his CV to make a better impression on employers. As a result there should be no unsuccessful game which comes right after successful one in his CV.
More formally, you are given an array s1, s2, ..., sn of zeros and ones. Zero corresponds to an unsuccessful game, one — to a successful one. Games are given in order they were produced, and Hideo can't swap these values. He should remove some elements from this array in such a way that no zero comes right after one.
Besides that, Hideo still wants to mention as much games in his CV as possible. Help this genius of a man determine the maximum number of games he can leave in his CV.
Input
The first line contains one integer number n (1 ≤ n ≤ 100).
The second line contains n space-separated integer numbers s1, s2, ..., sn (0 ≤ si ≤ 1). 0 corresponds to an unsuccessful game, 1 — to a successful one.
Output
Print one integer — the maximum number of games Hideo can leave in his CV so that no unsuccessful game comes after a successful one.
Examples
input
4
1 1 0 1
output
3
input
6
0 1 0 0 1 0
output
4
input
1
0
output
1
【翻译】给出一个长度为n的01序列，现在可以删除一些数，使得最终序列满足对于任何一个1后面所有位置都不会有0，求剩余元素个数的最大值。
题解：
①根据题目，可以的枚举哪个地方开始选择1，那么之后的0都要删除。
②实现方法是分别维护0和1的前缀，然后O(n)扫一遍就可以了。
#include<stdio.h>
#include<algorithm>
#define go(i,a,b) for(int i=a;i<=b;i++)
using namespace std;int n,ans,t,a[2][102];
int main()
{
scanf("%d",&n);
go(i,1,n)scanf("%d",&t),a[0][i]=a[0][i-1],a[1][i]=a[1][i-1],a[t][i]++;
go(i,1,n)if(a[1][i]!=a[1][i-1])ans=max(ans,a[0][i]+a[1][n]-a[1][i-1]);
ans=max(ans,a[0][n]);printf("%d
",ans);
return 0;
}//Paul_Guderian
这是1999年的冬天,从来没经历过的寒冷,
街边的楼群指着蓝天,人们都蜷缩在大衣里行色匆匆。——————汪峰《再见二十世纪》