Submission #1986433

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Source Code Expand

import java.util.HashSet;
import java.util.Set;

public class Main {

	private static void solve() {
		int n = ni();
		int m = ni();
		
		int[] count = new int[m];
		int[] samePair = new int[m];
		Set<Integer> set = new HashSet<>();
		for (int i = 0; i < n; i ++) {
			int x = ni();
			count[x % m] ++;
			if (set.contains(x)) {
				set.remove(x);
				samePair[x % m] ++;
			} else {
				set.add(x);
			}
		}
		
		int ret = count[0] / 2;
		count[0] %= 2;
		if (m % 2 == 0) {
			ret += count[m / 2] / 2;
			count[m / 2] %= 2;
		}
		for (int i = 1; i < (m + 1) / 2; i ++) {
			int v = Math.min(count[i], count[m - i]);
			ret += v;
			count[i] -= v;
			count[m - i] -= v;
		}
		for (int i = 0; i < m; i ++) {
			int v = Math.min(samePair[i], count[i] / 2);
			ret +=v;
		}
		System.out.println(ret);
	}

	public static void main(String[] args) {
		new Thread(null, new Runnable() {
			@Override
			public void run() {
				long start = System.currentTimeMillis();
				String debug = args.length > 0 ? args[0] : null;
				if (debug != null) {
					try {
						is = java.nio.file.Files.newInputStream(java.nio.file.Paths.get(debug));
					} catch (Exception e) {
						throw new RuntimeException(e);
					}
				}
				reader = new java.io.BufferedReader(new java.io.InputStreamReader(is), 32768);
				solve();
				out.flush();
				tr((System.currentTimeMillis() - start) + "ms");
			}
		}, "", 64000000).start();
	}

	private static java.io.InputStream is = System.in;
	private static java.io.PrintWriter out = new java.io.PrintWriter(System.out);
	private static java.util.StringTokenizer tokenizer = null;
	private static java.io.BufferedReader reader;

	public static String next() {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new java.util.StringTokenizer(reader.readLine());
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken();
	}

	private static double nd() {
		return Double.parseDouble(next());
	}

	private static long nl() {
		return Long.parseLong(next());
	}

	private static int[] na(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = ni();
		return a;
	}

	private static char[] ns() {
		return next().toCharArray();
	}

	private static long[] nal(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nl();
		return a;
	}

	private static int[][] ntable(int n, int m) {
		int[][] table = new int[n][m];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				table[i][j] = ni();
			}
		}
		return table;
	}

	private static int[][] nlist(int n, int m) {
		int[][] table = new int[m][n];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				table[j][i] = ni();
			}
		}
		return table;
	}

	private static int ni() {
		return Integer.parseInt(next());
	}

	private static void tr(Object... o) {
		if (is != System.in)
			System.out.println(java.util.Arrays.deepToString(o));
	}
}

Submission Info

Judge Result