From 04314cdd4a4e6375dc00d537d642fa43e428a541 Mon Sep 17 00:00:00 2001 From: yulin Date: Sun, 23 Nov 2025 23:37:30 +0800 Subject: [PATCH] fix(Arrangement): improve count and select methods with overflow checks and enhance documentation --- .../java/cn/hutool/core/math/Arrangement.java | 216 ++++++++++++++++-- .../cn/hutool/core/math/ArrangementTest.java | 130 +++++++++-- 2 files changed, 303 insertions(+), 43 deletions(-) diff --git a/hutool-core/src/main/java/cn/hutool/core/math/Arrangement.java b/hutool-core/src/main/java/cn/hutool/core/math/Arrangement.java index d04edc82d4..1ade5a3252 100644 --- a/hutool-core/src/main/java/cn/hutool/core/math/Arrangement.java +++ b/hutool-core/src/main/java/cn/hutool/core/math/Arrangement.java @@ -1,12 +1,9 @@ package cn.hutool.core.math; -import java.io.Serializable; -import java.util.ArrayList; -import java.util.Arrays; -import java.util.List; - import cn.hutool.core.util.ArrayUtil; -import cn.hutool.core.util.NumberUtil; + +import java.io.Serializable; +import java.util.*; /** * 排列A(n, m)
@@ -47,10 +44,23 @@ public class Arrangement implements Serializable { * @return 排列数 */ public static long count(int n, int m) { - if (n == m) { - return NumberUtil.factorial(n); + if (m < 0 || m > n) { + throw new IllegalArgumentException("n >= 0 && m >= 0 && m <= n required"); } - return (n > m) ? NumberUtil.factorial(n, n - m) : 0; + if (m == 0) { + return 1; + } + long result = 1; + // 从 n 到 n-m+1 逐个乘 + for (int i = 0; i < m; i++) { + long next = result * (n - i); + // 溢出检测 + if (next < result) { + throw new ArithmeticException("Overflow computing A(" + n + "," + m + ")"); + } + result = next; + } + return result; } /** @@ -77,26 +87,85 @@ public class Arrangement implements Serializable { } /** - * 排列选择（从列表中选择m个排列） + * 从当前数据中选择 m 个元素，生成所有「不重复」的排列（Permutation）。 * - * @param m 选择个数 - * @return 所有排列列表 + *

+ * 说明： + *

+ * + * 数量公式： + * 
+	 * A(n, m) = n! / (n - m)!
+	 *
+ * + * 举例： + * 
+	 * datas = ["1","2","3"]
+	 * m = 2
+	 * 输出：
+	 * ["1","2"]
+	 * ["1","3"]
+	 * ["2","1"]
+	 * ["2","3"]
+	 * ["3","1"]
+	 * ["3","2"]
+	 * 共 6 个（A(3,2)=6）
+	 *
+ * + * @param m 选择的元素个数 + * @return 所有长度为 m 的不重复排列列表 */ + public List select(int m) { - final List result = new ArrayList<>((int) count(this.datas.length, m)); - select(this.datas, new String[m], 0, result); + if (m < 0 || m > datas.length) { + return Collections.emptyList(); + } + if (m == 0) { + // A(n,0) = 1，唯一一个空排列 + return Collections.singletonList(new String[0]); + } + + long estimated = count(datas.length, m); + int capacity = estimated > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) estimated; + + List result = new ArrayList<>(capacity); + boolean[] visited = new boolean[datas.length]; + dfs(new String[m], 0, visited, result); return result; } + /** - * 排列所有组合，即A(n, 1) + A(n, 2) + A(n, 3)... + * 生成当前数据的全部不重复排列（长度为 1 至 n 的所有排列）。 * - * @return 全排列结果 + *

+ * 说明： + *

    + *
  • 不允许重复选择元素（无 ["1","1"]，无 ["2","2","3"] 这种）
    • + *
  • 包含所有长度 m=1..n 的排列
    • + *
  • 总数量为 A(n,1) + A(n,2) + ... + A(n,n)
    • + *
+ * + * 举例（datas = ["1","2","3"]）： + * 
+	 * m=1: ["1"], ["2"], ["3"]                             → 3 个
+	 * m=2: ["1","2"], ["1","3"], ["2","1"], ...            → 6 个
+	 * m=3: ["1","2","3"], ["1","3","2"], ["2","1","3"], ...→ 6 个
+	 *
+	 * 总共：3 + 6 + 6 = 15
+	 *
+ * + * @return 所有不重复排列列表 */ + public List selectAll() { - final List result = new ArrayList<>((int) countAll(this.datas.length)); - for (int i = 1; i <= this.datas.length; i++) { - result.addAll(select(i)); + List result = new ArrayList<>(); + for (int m = 1; m <= datas.length; m++) { + result.addAll(select(m)); } return result; } @@ -124,4 +193,113 @@ public class Arrangement implements Serializable { select(ArrayUtil.remove(datas, i), resultList, resultIndex + 1, result); } } + + /** + * 返回一个排列的迭代器 + * + * @param m 选择的元素个数 + * @return 排列迭代器 + */ + public Iterable iterate(int m) { + return () -> new ArrangementIterator(datas, m); + } + + + /** + * 排列迭代器 + * + * @author CherryRum + */ + private static class ArrangementIterator implements Iterator { + + private final String[] datas; + private final int m; + private final boolean[] visited; + private final String[] buffer; + private final Deque stack = new ArrayDeque<>(); + boolean end = false; + + ArrangementIterator(String[] datas, int m) { + this.datas = datas; + this.m = m; + this.visited = new boolean[datas.length]; + this.buffer = new String[m]; + // 初始化 dfs 栈 + stack.push(0); + } + + @Override + public boolean hasNext() { + return !end; + } + + @Override + public String[] next() { + while (!stack.isEmpty()) { + int depth = stack.size() - 1; + + int idx = stack.pop(); + if (idx >= datas.length) { + // 这一层遍历结束 + if (!stack.isEmpty()) { + int prev = stack.pop(); + stack.push(prev + 1); + } + continue; + } + + // 如果该元素未使用 + if (!visited[idx]) { + visited[idx] = true; + buffer[depth] = datas[idx]; + + if (depth == m - 1) { + // 输出一个排列 + visited[idx] = false; + + // 下一次从 idx+1 继续 + stack.push(idx + 1); + + return Arrays.copyOf(buffer, m); + } else { + // 继续下一层 + stack.push(idx + 1); // 当前层下一个起点 + stack.push(0); // 下一层起点 + continue; + } + } + + // 已访问则跳过 + stack.push(idx + 1); + } + + end = true; + return null; + } + } + + /** + * 核心递归方法（回溯算法） + * * @param current 当前构建的排列数组 + * + * @param depth 当前递归深度（填到了第几个位置） + * @param visited 标记数组，记录哪些索引已经被使用了 + * @param result 结果集 + */ + private void dfs(String[] current, int depth, boolean[] visited, List result) { + if (depth == current.length) { + result.add(Arrays.copyOf(current, current.length)); + return; + } + + for (int i = 0; i < datas.length; i++) { + if (!visited[i]) { + visited[i] = true; + current[depth] = datas[i]; + + dfs(current, depth + 1, visited, result); + visited[i] = false; + } + } + } } diff --git a/hutool-core/src/test/java/cn/hutool/core/math/ArrangementTest.java b/hutool-core/src/test/java/cn/hutool/core/math/ArrangementTest.java index 9819613d3c..b160d7fa29 100755 --- a/hutool-core/src/test/java/cn/hutool/core/math/ArrangementTest.java +++ b/hutool-core/src/test/java/cn/hutool/core/math/ArrangementTest.java @@ -1,20 +1,22 @@ package cn.hutool.core.math; +import cn.hutool.core.lang.Console; +import org.junit.jupiter.api.Disabled; +import org.junit.jupiter.api.Test; + import java.util.List; import static org.junit.jupiter.api.Assertions.*; -import org.junit.jupiter.api.Disabled; -import org.junit.jupiter.api.Test; - -import cn.hutool.core.lang.Console; /** * 排列单元测试 * @author looly - * */ public class ArrangementTest { + // ---------------------------------------------------- + // 基础测试 + // ---------------------------------------------------- @Test public void arrangementTest() { long result = Arrangement.count(4, 2); @@ -30,37 +32,117 @@ public class ArrangementTest { assertEquals(64, resultAll); } + // ---------------------------------------------------- + // select 基础测试 + // ---------------------------------------------------- @Test public void selectTest() { - Arrangement arrangement = new Arrangement(new String[] { "1", "2", "3", "4" }); + Arrangement arrangement = new Arrangement(new String[]{"1", "2", "3", "4"}); List list = arrangement.select(2); - assertEquals(Arrangement.count(4, 2), list.size()); - assertArrayEquals(new String[] {"1", "2"}, list.get(0)); - assertArrayEquals(new String[] {"1", "3"}, list.get(1)); - assertArrayEquals(new String[] {"1", "4"}, list.get(2)); - assertArrayEquals(new String[] {"2", "1"}, list.get(3)); - assertArrayEquals(new String[] {"2", "3"}, list.get(4)); - assertArrayEquals(new String[] {"2", "4"}, list.get(5)); - assertArrayEquals(new String[] {"3", "1"}, list.get(6)); - assertArrayEquals(new String[] {"3", "2"}, list.get(7)); - assertArrayEquals(new String[] {"3", "4"}, list.get(8)); - assertArrayEquals(new String[] {"4", "1"}, list.get(9)); - assertArrayEquals(new String[] {"4", "2"}, list.get(10)); - assertArrayEquals(new String[] {"4", "3"}, list.get(11)); + // 校验数量一致 + assertEquals(Arrangement.count(4, 2), list.size()); + + // 逐项严格校验顺序是否一致（按 DFS 顺序） + assertArrayEquals(new String[]{"1", "2"}, list.get(0)); + assertArrayEquals(new String[]{"1", "3"}, list.get(1)); + assertArrayEquals(new String[]{"1", "4"}, list.get(2)); + assertArrayEquals(new String[]{"2", "1"}, list.get(3)); + assertArrayEquals(new String[]{"2", "3"}, list.get(4)); + assertArrayEquals(new String[]{"2", "4"}, list.get(5)); + assertArrayEquals(new String[]{"3", "1"}, list.get(6)); + assertArrayEquals(new String[]{"3", "2"}, list.get(7)); + assertArrayEquals(new String[]{"3", "4"}, list.get(8)); + assertArrayEquals(new String[]{"4", "1"}, list.get(9)); + assertArrayEquals(new String[]{"4", "2"}, list.get(10)); + assertArrayEquals(new String[]{"4", "3"}, list.get(11)); + + // 测试 selectAll List selectAll = arrangement.selectAll(); assertEquals(Arrangement.countAll(4), selectAll.size()); + // m=0，应该返回一个空排列 List list2 = arrangement.select(0); assertEquals(1, list2.size()); + assertEquals(0, list2.get(0).length); } + // ---------------------------------------------------- + // 扩展测试：边界、错误处理 + // ---------------------------------------------------- @Test - @Disabled - public void selectTest2() { - List list = MathUtil.arrangementSelect(new String[] { "1", "1", "3", "4" }); - for (String[] strings : list) { - Console.log(strings); + public void boundaryTest() { + Arrangement arr = new Arrangement(new String[]{"A", "B", "C"}); + + // m = n + List full = arr.select(3); + assertEquals(6, full.size()); + + // m = 1 + List one = arr.select(1); + assertEquals(3, one.size()); + assertArrayEquals(new String[]{"A"}, one.get(0)); + + // m > n → empty list + assertTrue(arr.select(10).isEmpty()); + + // m < 0 → empty list + assertTrue(arr.select(-1).isEmpty()); + } + + // ---------------------------------------------------- + // 扩展测试：空数组 + // ---------------------------------------------------- + @Test + public void emptyTest() { + Arrangement arrangement = new Arrangement(new String[]{}); + + assertEquals(1, arrangement.select(0).size()); + assertTrue(arrangement.select(1).isEmpty()); + assertTrue(arrangement.selectAll().isEmpty()); // A(0,m) = 0 for m>0，A(0,0)=1 → 全排列 = 1 个空排列 + } + + // ---------------------------------------------------- + // 扩展测试：重复元素（用于验证去重算法） + // 默认 Arrangement 不去重，因此应该包含重复排列 + // ---------------------------------------------------- + @Test + @Disabled("默认 Arrangement 不支持去重；启用后手动检查") + public void duplicateElementTest() { + Arrangement arrangement = new Arrangement(new String[]{"1", "1", "3"}); + + List list = arrangement.select(2); + + // 应该有 A(3,2) = 6 个 + assertEquals(6, list.size()); + + for (String[] s : list) { + Console.log(s); } } + + // ---------------------------------------------------- + // 扩展测试：selectAll 覆盖全部不重复排列（A(n,1..n)） + // ---------------------------------------------------- + @Test + public void selectAllTest() { + Arrangement arrangement = new Arrangement(new String[]{"1", "2", "3"}); + + List all = arrangement.selectAll(); + + // 打印用于观测 + for (String[] s : all) { + Console.log(s); + } + + // A(3,1) + A(3,2) + A(3,3) = 3 + 6 + 6 = 15 + assertEquals(Arrangement.countAll(3), all.size()); + assertEquals(15, all.size()); + + // spot check 不重复排列 + assertArrayEquals(new String[]{"1"}, all.get(0)); + assertArrayEquals(new String[]{"1", "2"}, all.get(3)); + assertArrayEquals(new String[]{"1", "2", "3"}, all.get(9)); + } + }