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71 lines
1.6 KiB
Java
71 lines
1.6 KiB
Java
import java.util.*;
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public class ArrayRotate {
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public static void rotate1(int[] a, int first, int middle, int last) {
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int next = middle;
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while (first != next) {
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swap(a, first++, next++);
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if (next == last)
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next = middle;
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else if (first == middle)
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middle = next;
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}
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}
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public static void rotate2(int[] a, int first, int middle, int last) {
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reverse(a, first, middle);
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reverse(a, middle, last);
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reverse(a, first, last);
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}
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static void reverse(int[] a, int from, int to) {
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while (from < --to)
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swap(a, from++, to);
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}
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public static void rotate3(int[] a, int first, int middle, int last) {
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int n = last - first;
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int jump = middle - first;
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int gcd = gcd(jump, n);
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int cycle = n / gcd;
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for (int i = 0; i < gcd; i++) {
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for (int j = 0, cur = i; j < cycle - 1; j++) {
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int next = cur + jump;
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if (next >= n)
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next -= n;
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swap(a, cur, next);
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cur = next;
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}
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}
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}
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static int gcd(int a, int b) {
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return a == 0 ? b : gcd(b % a, a);
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}
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static void swap(int[] a, int i, int j) {
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int t = a[j];
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a[j] = a[i];
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a[i] = t;
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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(10) + 1;
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int middle = rnd.nextInt(n);
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int[] a = rnd.ints(n, 0, 10).toArray();
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int[] b1 = a.clone();
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rotate1(b1, 0, middle, n);
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int[] b2 = a.clone();
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rotate2(b2, 0, middle, n);
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int[] b3 = a.clone();
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rotate3(b3, 0, middle, n);
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if (!Arrays.equals(b1, b2) || !Arrays.equals(b1, b3))
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throw new RuntimeException();
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}
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}
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}
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