71 lines
1.8 KiB
Java
71 lines
1.8 KiB
Java
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import java.util.*;
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public class MaximumZeroSubmatrix {
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public static int maximumZeroSubmatrix(int[][] a) {
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int R = a.length;
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int C = a[0].length;
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int res = 0;
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int[] d = new int[C];
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Arrays.fill(d, -1);
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int[] d1 = new int[C];
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int[] d2 = new int[C];
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int[] st = new int[C];
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for (int r = 0; r < R; ++r) {
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for (int c = 0; c < C; ++c)
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if (a[r][c] == 1)
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d[c] = r;
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int size = 0;
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for (int c = 0; c < C; ++c) {
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while (size > 0 && d[st[size - 1]] <= d[c]) --size;
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d1[c] = size == 0 ? -1 : st[size - 1];
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st[size++] = c;
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}
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size = 0;
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for (int c = C - 1; c >= 0; --c) {
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while (size > 0 && d[st[size - 1]] <= d[c]) --size;
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d2[c] = size == 0 ? C : st[size - 1];
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st[size++] = c;
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}
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for (int j = 0; j < C; ++j)
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res = Math.max(res, (r - d[j]) * (d2[j] - d1[j] - 1));
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}
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return res;
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}
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// random test
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public static void main(String[] args) {
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Random rnd = new Random(1);
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for (int step = 0; step < 1000; step++) {
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int R = rnd.nextInt(10) + 1;
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int C = rnd.nextInt(10) + 1;
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int[][] a = new int[R][C];
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for (int r = 0; r < R; r++)
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for (int c = 0; c < C; c++)
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a[r][c] = rnd.nextInt(2);
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int res1 = maximumZeroSubmatrix(a);
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int res2 = slowMaximumZeroSubmatrix(a);
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if (res1 != res2)
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throw new RuntimeException(res1 + " " + res2);
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}
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}
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static int slowMaximumZeroSubmatrix(int[][] a) {
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int res = 0;
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int R = a.length;
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int C = a[0].length;
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for (int r2 = 0; r2 < R; r2++)
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for (int c2 = 0; c2 < C; c2++)
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for (int r1 = 0; r1 <= r2; r1++)
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m1:for (int c1 = 0; c1 <= c2; c1++) {
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for (int r = r1; r <= r2; r++)
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for (int c = c1; c <= c2; c++)
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if (a[r][c] != 0)
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continue m1;
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res = Math.max(res, (r2 - r1 + 1) * (c2 - c1 + 1));
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}
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return res;
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}
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}
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