46 lines
1.0 KiB
Java
46 lines
1.0 KiB
Java
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import java.util.*;
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import java.util.stream.Stream;
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public class GraphColoringGreedy2 {
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public static int[] color(List<Integer>[] graph) {
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int n = graph.length;
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int[] used = new int[n];
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int[] colors = new int[n];
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Arrays.fill(colors, -1);
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for (int i = 0; i < n; i++) {
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int best_cnt = -1;
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int bestu = -1;
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for (int u = 0; u < n; u++) {
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if (colors[u] == -1) {
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int cnt = Integer.bitCount(used[u]);
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if (best_cnt < cnt) {
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best_cnt = cnt;
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bestu = u;
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}
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}
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}
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int c = Integer.numberOfTrailingZeros(~used[bestu]);
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colors[bestu] = c;
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for (int v : graph[bestu]) {
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used[v] |= 1 << c;
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}
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}
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return colors;
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}
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// Usage example
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public static void main(String[] args) {
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int n = 5;
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List<Integer>[] g = Stream.generate(ArrayList::new).limit(n).toArray(List[]::new);
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for (int i = 0; i < n; i++) {
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for (int j = 0; j < n; j++) {
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g[i].add((i + 1) % n);
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g[(i + 1) % n].add(i);
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}
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}
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System.out.println(Arrays.toString(color(g)));
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}
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}
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