RT，觉得已经写的没问题了，但是还是样例过不去，求助dalao

#include <iostream>

using namespace std;

int n ,a[1005] ,dp[1005][1005] ,ans=0 ; 

// dp[i][j]表示的是数列第i位放的是原数组的j位的数组 

int main () {
    cin >> n ;

    for ( int i = 1 ;i <= n; i++ ) 
        cin >> a[i] ;

    dp[0][0] = 0 ;

    for ( int i = 1 ; i <= n; i++ )
        for ( int j = 1; j <= n; j++ ) {
            if( a[j] == i )
                dp[i][j] = max (dp[i][j], max(dp[i][j-1], dp[i-1][j-1] + 1 ) ) ;
            else
                dp[i][j] = max (dp[i][j], dp[i][j-1] ) ;

            ans = max ( ans, dp[i][j] ) ;
        }

    cout << ans ;

    return 0 ;
}