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import java.io.*; import java.util.*; public clas...

Created on: July 5, 2025

Answered using O4 Mini High by Chat01

Question

import java.io.;
import java.util.;

public class Main {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int T = Integer.parseInt(br.readLine());
StringBuilder sb = new StringBuilder();
while (T-- > 0) {
StringTokenizer st = new StringTokenizer(br.readLine());
int n = Integer.parseInt(st.nextToken());
int m = Integer.parseInt(st.nextToken());

text
        long[] dp = new long[n+1];
        dp[0] = 1;

        for (int p = n; p >= 1; p--) {
            long[] next = new long[n+1];
            int done = n - p + 1;

            for (int t = 0; t <= done; t++) {
                long cur = dp[t];
                if (cur == 0) continue;

                next[t] = (next[t] + cur) % m;

                int avail = done - t;
                if (avail > 0) {
                    next[t+1] = (next[t+1] + cur * avail % m * p) % m;
                }
            }

            dp = next;
        }

        long total = 0;
        for (long x : dp) {
            total = (total + x) % m;
        }
        sb.append(total).append('\n');
    }
    System.out.print(sb);
}

}
can we simplify this code

Thought

Simplifying code

The user wants to simplify Java code, so my goal is to suggest ways to make the algorithm more efficient. I could combine loops, reuse the DP array, and minimize memory usage, avoiding the creation of new arrays. A potential solution is updating the array in place and reducing complexity. I could also suggest renaming variables, adding comments, and optimizing the performance. Precomputing factorial values might help in some cases, but since m isn't prime, I’d need to adjust the approach for using combinations and modular operations.

Thought for a couple of seconds

Answer

Here’s a cleaned‐up, more concise version of your DP solution that:

  • Eliminates the extra array allocation inside the loop by reusing a single “next” buffer.
  • Simplifies input parsing with a tiny FastReader.
  • Clarifies variable names and inlines “done” where it’s used.
java
import java.io.*;
import java.util.*;

public class Main {
    static class FastReader {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String next() throws IOException {
            String s; 
            while ((s = br.readLine()) != null && s.isEmpty()) {}
            return s;
        }
        int nextInt() throws IOException {
            return Integer.parseInt(next().trim().split("\\s+")[0]);
        }
    }

    public static void main(String[] args) throws IOException {
        FastReader in = new FastReader();
        int T = in.nextInt();
        StringBuilder out = new StringBuilder();
        while (T-- > 0) {
            String[] nm = in.next().trim().split("\\s+");
            int n = Integer.parseInt(nm[0]), mod = Integer.parseInt(nm[1]);

            long[] dp = new long[n + 1];
            long[] next = new long[n + 1];
            dp[0] = 1;

            // Place values p = n, n-1, ..., 1
            for (int p = n; p >= 1; p--) {
                Arrays.fill(next, 0);
                // done = how many positions already filled:  n - p + 1
                int done = n - p + 1;
                for (int taken = 0; taken <= done; taken++) {
                    long ways = dp[taken];
                    if (ways == 0) continue;
                    // Option 1: leave the new slot empty
                    next[taken] = (next[taken] + ways) % mod;
                    // Option 2: fill one of the (done - taken) free slots with one of p items
                    int free = done - taken;
                    if (free > 0) {
                        next[taken + 1] = (next[taken + 1] + ways * free % mod * p) % mod;
                    }
                }
                // swap dp and next
                long[] tmp = dp; 
                dp = next; 
                next = tmp;
            }

            // sum up all ways
            long total = 0;
            for (long w : dp) total = (total + w) % mod;
            out.append(total).append('\n');
        }
        System.out.print(out);
    }
}

What’s improved?

  1. FastReader
    • Reads full lines and splits once, avoiding StringTokenizer.
  2. Array reuse
    • next is allocated just once outside the loop and zeroed via Arrays.fill(), saving GC churn.
  3. Clearer names
    • taken instead of t, ways instead of cur, free instead of avail.
  4. Swap trick
    • Swapping the references dp and next to avoid repeated allocations.

This version behaves identically but is shorter, easier to read, and marginally faster by reusing memory.

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