64 lines
1.3 KiB
Java
64 lines
1.3 KiB
Java
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import java.util.*;
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public class RandomPermutation {
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public static void shuffle(int[] a) {
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Random rnd = new Random();
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for (int i = a.length - 1; i >= 1; i--) {
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int j = rnd.nextInt(i + 1);
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int t = a[i];
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a[i] = a[j];
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a[j] = t;
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}
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}
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public static int[] getRandomPermutation(int n) {
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Random rnd = new Random();
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int[] res = new int[n];
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for (int i = 0; i < n; i++) {
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int j = rnd.nextInt(i + 1);
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res[i] = res[j];
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res[j] = i;
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}
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return res;
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}
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public static int[] getRandomArrangement(int n, int m) {
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Random rnd = new Random();
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int[] res = new int[n];
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for (int i = 0; i < n; i++)
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res[i] = i;
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for (int i = 0; i < m; i++) {
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int j = i + rnd.nextInt(n - i);
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int t = res[i];
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res[i] = res[j];
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res[j] = t;
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}
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return Arrays.copyOf(res, m);
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}
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public static int[] getRandomCombination(int n, int m) {
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int[] res = getRandomArrangement(n, m);
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Arrays.sort(res);
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return res;
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}
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// for small m
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public static int[] getRandomArrangement2(int n, int m) {
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Random rnd = new Random();
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Set<Integer> set = new HashSet<>();
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int[] res = new int[m];
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while (set.size() < m) {
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int x = rnd.nextInt(n);
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if (set.add(x))
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res[set.size() - 1] = x;
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}
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return res;
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}
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// Usage example
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public static void main(String[] args) {
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System.out.println(Arrays.toString(getRandomPermutation(5)));
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}
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}
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