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63 lines
1.5 KiB
Java
63 lines
1.5 KiB
Java
import java.util.*;
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public class Mis {
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public static int mis(BitSet[] g, BitSet unused) {
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int v = -1;
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for (int u = unused.nextSetBit(0); u >= 0; u = unused.nextSetBit(u + 1))
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if (v == -1 || g[v].cardinality() > g[u].cardinality())
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v = u;
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if (v == -1)
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return 0;
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int res = -1;
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BitSet nv = (BitSet) g[v].clone();
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nv.and(unused);
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for (int y = nv.nextSetBit(0); y >= 0; y = nv.nextSetBit(y + 1)) {
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BitSet newUnused = (BitSet) unused.clone();
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newUnused.andNot(g[y]);
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res = Math.max(res, 1 + mis(g, newUnused));
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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 n = rnd.nextInt(16) + 1;
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BitSet[] g = new BitSet[n];
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for (int i = 0; i < g.length; i++) {
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g[i] = new BitSet(n);
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// for convenience of mis()
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g[i].set(i);
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}
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for (int i = 0; i < n; i++)
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for (int j = 0; j < i; j++)
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if (rnd.nextBoolean()) {
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g[i].set(j);
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g[j].set(i);
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}
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BitSet unused = new BitSet();
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unused.set(0, n);
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int res1 = mis(g, unused);
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int res2 = misSlow(g);
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if (res1 != res2)
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throw new RuntimeException();
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}
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}
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static int misSlow(BitSet[] g) {
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int res = 0;
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int n = g.length;
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for (int set = 0; set < 1 << n; set++) {
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boolean ok = true;
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for (int i = 0; i < n; i++)
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for (int j = 0; j < i; j++)
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ok &= (set & (1 << i)) == 0 || (set & (1 << j)) == 0 || !g[i].get(j);
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if (ok)
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res = Math.max(res, Integer.bitCount(set));
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}
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return res;
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}
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}
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