【东莞市选2007】拦截导弹

https://jzoj.net/senior/#main/show/1003

简单dp，O(n^2)

#include<iostream>
#include<cstring>
#include<cstdio>

using namespace std;

inline int rd(){
    int ret=0,f=1;char c;
    while(c=getchar(),!isdigit(c))f=c=='-'?-1:1;
    while(isdigit(c))ret=ret*10+c-'0',c=getchar();
    return ret*f;
}

const int MAXN=1024;

int n,T;
int h[MAXN],f[MAXN][2];

void init(){
    memset(f,0,sizeof(f));
    h[0]=-1;
}

void solve(){
    int ans=0;
    for(int i=1;i<=n;i++) h[i]=rd();
    for(int i=1;i<=n;i++){
        for(int j=0;j<i;j++){
            if(h[j]==h[i]) continue;
            if(h[j]<h[i]) f[i][1]=max(f[i][1],f[j][0]+1);
            else f[i][0]=max(f[i][0],f[j][1]+1);
            ans=max(ans,max(f[i][0],f[i][1]));
        }
    }
    printf("%d
",ans);
}


int main(){
    while(n=rd()){
        init();
        solve();
    }
    return 0;
}