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https://gitee.com/chinabugotech/hutool.git
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Golden Looly
GitHub
commit
1d9b0ebbd2
@ -213,68 +213,147 @@ public class Arrangement implements Serializable {
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private static class ArrangementIterator implements Iterator<String[]> {
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private final String[] datas;
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private final int n;
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private final int m;
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private final boolean[] visited;
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private final String[] buffer;
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private final Deque<Integer> stack = new ArrayDeque<>();
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boolean end = false;
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// 每一层记录当前尝试的下标，-1表示还未尝试
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private final int[] indices;
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private int depth;
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private boolean end;
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// 预取下一个元素
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private String[] nextItem;
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private boolean nextPrepared;
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ArrangementIterator(String[] datas, int m) {
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this.datas = datas;
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this.n = datas.length;
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this.m = m;
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this.visited = new boolean[datas.length];
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this.buffer = new String[m];
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// 初始化 dfs 栈
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stack.push(0);
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this.visited = new boolean[n];
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this.nextItem = null;
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this.nextPrepared = false;
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if (m < 0 || m > n) {
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// 无效或无解，直接结束
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this.indices = new int[Math.max(1, m)];
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this.buffer = new String[Math.max(1, m)];
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this.depth = -1;
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this.end = true;
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} else if (m == 0) {
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// m == 0: 只返回一个空数组
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this.indices = new int[0];
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this.buffer = new String[0];
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this.depth = 0;
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this.end = false;
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} else {
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this.indices = new int[m];
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Arrays.fill(this.indices, -1);
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this.buffer = new String[m];
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this.depth = 0;
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this.end = false;
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}
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}
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@Override
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public boolean hasNext() {
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return !end;
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if (end) return false;
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if (nextPrepared) return nextItem != null;
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prepareNext();
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return nextItem != null;
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}
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@Override
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public String[] next() {
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while (!stack.isEmpty()) {
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int depth = stack.size() - 1;
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if (end && !nextPrepared) {
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throw new NoSuchElementException();
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}
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if (!nextPrepared) {
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prepareNext();
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}
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if (nextItem == null) {
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throw new NoSuchElementException();
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}
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String[] ret = nextItem;
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// 清除预取缓存，下一次需要重新准备
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nextItem = null;
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nextPrepared = false;
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// 如果m == 0，该项是唯一项，迭代结束
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if (m == 0) {
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end = true;
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}
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return ret;
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}
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int idx = stack.pop();
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if (idx >= datas.length) {
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// 这一层遍历结束
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if (!stack.isEmpty()) {
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int prev = stack.pop();
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stack.push(prev + 1);
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/**
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* 将状态推进到下一个可返回的排列并把它放入 nextItem。
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* 如果无更多排列，则将 end=true 并把 nextItem 置为 null。
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*/
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private void prepareNext() {
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// 已经准备过或已结束
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if (nextPrepared || end) {
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nextPrepared = true;
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return;
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}
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// special-case m == 0
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if (m == 0) {
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nextItem = new String[0];
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nextPrepared = true;
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// do not set end here; end will be set after returning this element in next()
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return;
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}
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// 非递归模拟DFS，直到找到一个可返回的排列或穷尽
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while (depth >= 0) {
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int start = indices[depth] + 1;
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boolean found = false;
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for (int i = start; i < n; i++) {
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if (!visited[i]) {
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// 如果当前层之前有选过一个元素，要先取消之前选中的 visited
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if (indices[depth] != -1) {
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visited[indices[depth]] = false;
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}
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indices[depth] = i;
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visited[i] = true;
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buffer[depth] = datas[i];
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found = true;
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break;
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}
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}
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if (!found) {
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// 本层没有可用元素，回溯
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if (indices[depth] != -1) {
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visited[indices[depth]] = false;
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indices[depth] = -1;
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}
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depth--;
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continue;
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}
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// 如果该元素未使用
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if (!visited[idx]) {
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visited[idx] = true;
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buffer[depth] = datas[idx];
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if (depth == m - 1) {
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// 输出一个排列
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visited[idx] = false;
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// 下一次从 idx+1 继续
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stack.push(idx + 1);
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return Arrays.copyOf(buffer, m);
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} else {
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// 继续下一层
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stack.push(idx + 1); // 当前层下一个起点
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stack.push(0); // 下一层起点
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continue;
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// 若已达到输出深度，准备输出（但不抛出）
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if (depth == m - 1) {
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nextItem = Arrays.copyOf(buffer, m);
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// 取消当前visited，为下一次在同一层寻找下一个候选做准备
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visited[indices[depth]] = false;
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// 保持 depth 不变（下一次 prepare 会从 indices[depth]+1 开始寻找）
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nextPrepared = true;
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return;
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} else {
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// 向下一层深入：初始化下一层为-1并继续循环
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depth++;
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if (depth < m) {
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indices[depth] = -1;
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}
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}
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// 已访问则跳过
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stack.push(idx + 1);
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}
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// 若循环结束，说明已经穷尽所有可能
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end = true;
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return null;
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nextItem = null;
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nextPrepared = true;
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}
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}
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@ -4,6 +4,7 @@ import cn.hutool.core.lang.Console;
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import org.junit.jupiter.api.Disabled;
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import org.junit.jupiter.api.Test;
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import java.util.ArrayList;
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import java.util.List;
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import static org.junit.jupiter.api.Assertions.*;
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@ -145,4 +146,51 @@ public class ArrangementTest {
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assertArrayEquals(new String[]{"1", "2", "3"}, all.get(9));
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}
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// ----------------------------------------------------
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// 迭代器测试
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// ----------------------------------------------------
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@Test
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public void iteratorTest() {
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Arrangement arrangement = new Arrangement(new String[]{"1", "2", "3"});
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// 测试 m=2 的情况
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List<String[]> iterResult = new ArrayList<>();
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for (String[] perm : arrangement.iterate(2)) {
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iterResult.add(perm);
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}
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assertEquals(6, iterResult.size());
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assertArrayEquals(new String[]{"1", "2"}, iterResult.get(0));
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assertArrayEquals(new String[]{"1", "3"}, iterResult.get(1));
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assertArrayEquals(new String[]{"2", "1"}, iterResult.get(2));
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assertArrayEquals(new String[]{"2", "3"}, iterResult.get(3));
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assertArrayEquals(new String[]{"3", "1"}, iterResult.get(4));
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assertArrayEquals(new String[]{"3", "2"}, iterResult.get(5));
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}
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@Test
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public void iteratorFullTest() {
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Arrangement arrangement = new Arrangement(new String[]{"1", "2", "3"});
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// 测试全排列的情况
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List<String[]> iterResult = new ArrayList<>();
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for (String[] perm : arrangement.iterate(3)) {
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iterResult.add(perm);
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}
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assertEquals(6, iterResult.size());
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}
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@Test
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public void iteratorBoundaryTest() {
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Arrangement arrangement = new Arrangement(new String[]{"1", "2", "3"});
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// 测试 m > n 的情况
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List<String[]> iterResult = new ArrayList<>();
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for (String[] perm : arrangement.iterate(5)) {
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iterResult.add(perm);
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}
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assertTrue(iterResult.isEmpty());
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}
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}
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