P1410 子序列

#include <bits/stdc++.h>
# define LL long
using namespace std;

int n;
int a[2001];
int col[2001];

struct Edge{
    int to;
    int next;
}e[2001*2001];
int head[2001];
int en;

void add(int from, int to){
    e[en].next=head[from];
    e[en].to=to;
    head[from]=en;
    ++en;
}

bool dfs(int u, int color){
    if(col[u]!=-1 && col[u]!=color) return false;
    if(col[u]!=-1 && col[u]==color) return true;
    col[u]=color;
    for(int i=head[u];i!=-1;i=e[i].next){
        int v=e[i].to;
        if(!dfs(v,1-color)) return false;
    }
    return true;
}

int main(){
    while(scanf("%d", &n)!=EOF){
        memset(head,-1,sizeof(head));
        en=0;
        for(int i=1;i<=n;++i){
            scanf("%d", a+i);
        }
        memset(col,-1,sizeof(col));
        for(int i=1;i<=n;++i){
            for(int j=i+1;j<=n;++j){
                if(a[i]>=a[j]){
                    add(i,j);
                    add(j,i);
                }
            }
        }
        int valid=1;
        for(int i=1;i<=n;++i){
            if(col[i]==-1){
                if(!dfs(i,0)) {
                    valid=0;
                    break;
                }
            }
        }
        if(valid==0) printf("No!\n");
        else printf("Yes!\n");
    }
    return 0;
}

#include <bits/stdc++.h>
# define LL long
using namespace std;

const int INF=0x7fffffff;
int n;
int a[2001];
int f[2001][2001];

int main(){
    while(scanf("%d", &n)!=EOF){
        for(int i=1;i<=n;++i){
            scanf("%d", a+i);
        }
        for(int i=1;i<=n;++i){
            for(int j=1;j<=i;++j){
                f[i][j]=INF;
            }
        }
        f[1][1]=-1;
        for(int i=1;i<=n;++i){
            for(int j=1;j<=i;++j){
                if(f[i][j]<INF){
                    if(a[i+1]>a[i]){
                        f[i+1][j+1]=min(f[i+1][j+1],f[i][j]);
                    }
                    if(a[i+1]>f[i][j]){
                        f[i+1][i-j+1]=min(f[i+1][i-j+1],a[i]);
                    }
                }
            }
        }
        if(f[n][n/2]==INF) printf("No!\n");
        else printf("Yes!\n");
    }
    return 0;
}