From ede848ed0767672fb6daea9bb0c73a195396655d Mon Sep 17 00:00:00 2001
From: Looly <loolly@aliyun.com>
Date: Sun, 29 Sep 2024 16:19:07 +0800
Subject: [PATCH] add CollStreamUtil

---
 .../core/collection/CollStreamUtil.java       | 22 +++++++++++++++++++
 .../core/collection/CollStreamUtilTest.java   | 21 +++++++++++++++++-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/hutool-core/src/main/java/org/dromara/hutool/core/collection/CollStreamUtil.java b/hutool-core/src/main/java/org/dromara/hutool/core/collection/CollStreamUtil.java
index 188d83225..06978d628 100644
--- a/hutool-core/src/main/java/org/dromara/hutool/core/collection/CollStreamUtil.java
+++ b/hutool-core/src/main/java/org/dromara/hutool/core/collection/CollStreamUtil.java
@@ -29,6 +29,7 @@ import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Collector;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * 集合的stream操作封装
@@ -396,4 +397,25 @@ public class CollStreamUtil {
 		}
 		return map;
 	}
+
+	/**
+	 * 笛卡尔积<br>
+	 * 参考：https://www.baeldung-cn.com/java-cartesian-product-sets
+	 *
+	 * @param sets  集合列表
+	 * @param index 索引
+	 * @return 笛卡尔积
+	 */
+	public static Stream<List<Object>> cartesianProduct(final List<List<Object>> sets, final int index) {
+		if (index == sets.size()) {
+			return Stream.of(ListUtil.zero());
+		}
+		final List<Object> currentSet = sets.get(index);
+		return currentSet.stream().flatMap(element -> cartesianProduct(sets, index + 1)
+			.map(list -> {
+				final List<Object> newList = new ArrayList<>(list);
+				newList.add(0, element);
+				return newList;
+			}));
+	}
 }
diff --git a/hutool-core/src/test/java/org/dromara/hutool/core/collection/CollStreamUtilTest.java b/hutool-core/src/test/java/org/dromara/hutool/core/collection/CollStreamUtilTest.java
index c4b8c8f5e..2554d318e 100644
--- a/hutool-core/src/test/java/org/dromara/hutool/core/collection/CollStreamUtilTest.java
+++ b/hutool-core/src/test/java/org/dromara/hutool/core/collection/CollStreamUtilTest.java
@@ -16,10 +16,10 @@
 
 package org.dromara.hutool.core.collection;
 
-import org.dromara.hutool.core.map.MapUtil;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.ToString;
+import org.dromara.hutool.core.map.MapUtil;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
@@ -320,6 +320,25 @@ public class CollStreamUtilTest {
 		}
 	}
 
+	@Test
+	void cartesianProductTest() {
+		final List<List<Object>> sets = new ArrayList<>();
+		sets.add(ListUtil.of(10, 20));
+		sets.add(ListUtil.of("John", "Jack"));
+		sets.add(ListUtil.of('I', 'J'));
+
+		final List<List<Object>> collect = CollStreamUtil.cartesianProduct(sets, 0).collect(Collectors.toList());
+		Assertions.assertEquals(8, collect.size());
+		Assertions.assertEquals("[10, John, I]", collect.get(0).toString());
+		Assertions.assertEquals("[10, John, J]", collect.get(1).toString());
+		Assertions.assertEquals("[10, Jack, I]", collect.get(2).toString());
+		Assertions.assertEquals("[10, Jack, J]", collect.get(3).toString());
+		Assertions.assertEquals("[20, John, I]", collect.get(4).toString());
+		Assertions.assertEquals("[20, John, J]", collect.get(5).toString());
+		Assertions.assertEquals("[20, Jack, I]", collect.get(6).toString());
+		Assertions.assertEquals("[20, Jack, J]", collect.get(7).toString());
+	}
+
 	/**
 	 * 班级类
 	 */