백준 1932번의 동적계획법 문제를 풀었는데요

#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
 
int cost[1001][501];
int dp[1001][501];
int N;
 
int dfs(int pre, int max_idx) {
    if(max_idx >= N)
        return 0;
    if(dp[pre][max_idx] != -1)
        return dp[pre][max_idx];
    int m = 0;
    m = max(m,cost[pre][max_idx] + dfs(pre,max_idx+1));
    m = max(m,cost[pre][max_idx] + dfs(pre+1,max_idx+1));
    dp[pre][max_idx] = m;
 
    return m;
}
 
int main()
{
    scanf("%d",&N);
    for(int i=0; i<N; i++)
        for(int j=0; j<=i; j++)
            scanf("%d",&cost[j][i]);
    memset(dp,-1,sizeof(dp));
    printf("%d\n",dfs(0,0));
    return 0;
}