diff --git a/history/010_tree_grow/src/main/java/com/gitee/drinkjava2/frog/util/RandomUtils.java b/history/010_tree_grow/src/main/java/com/gitee/drinkjava2/frog/util/RandomUtils.java
new file mode 100644
index 0000000..dff7533
--- /dev/null
+++ b/history/010_tree_grow/src/main/java/com/gitee/drinkjava2/frog/util/RandomUtils.java
@@ -0,0 +1,101 @@
+/* Copyright 2018-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by
+ * applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS
+ * OF ANY KIND, either express or implied. See the License for the specific
+ * language governing permissions and limitations under the License.
+ */
+package com.gitee.drinkjava2.frog.util;
+
+import java.util.Random;
+
+/**
+ * Random Utilities used in this project
+ * 
+ * @author Yong Zhu
+ * @since 1.0
+ */
+public class RandomUtils {
+
+    private RandomUtils() {
+    }
+
+    private static final Random rand = new Random();
+
+    public static int nextInt(int i) {//返回随机整数，最小为0，最大为n-1
+        if(i==0)
+            return 0;
+        return rand.nextInt(i);
+    }
+    
+    public static int nextNegOrPosInt(int n) {//返回随机整数，最小为-(n-1)，最大为n-1
+        int x = nextInt(n);
+        if (percent(50))
+            return x;
+        return -x;
+    }
+
+    public static float nextFloat() {
+        return rand.nextFloat();
+    }
+
+    public static boolean percent(float percent) {// 有百分这percent的机率为true
+        return rand.nextFloat() * 100 < percent;
+    }
+
+    public static int vary(int v, int percet) {
+        if (percent(percet))
+            return vary(v);
+        return v;
+    }
+
+    public static int vary(int v) {// 随机有大概率小变异，小概率大变异，极小概率极大变异
+        if (percent(40))
+            v += v * .04 * (nextFloat() - 0.5); // v=v+-.04
+        if (percent(10))
+            v += v * .103 * (nextFloat() - 0.5); // v=v+-0.1
+        else if (percent(5))
+            v += v * 1 * (nextFloat() - 0.5); // v=v+-0.4
+        else if (percent(2))
+            v += v * 4 * (nextFloat() - 0.5); // v=v+-2
+        else if (percent(1f))
+            v += v * 8 * (nextFloat() - 0.5); // v=v+-6
+        return v;
+    }
+
+    public static float vary(float v) {// 随机有大概率小变异，小概率大变异，极小概率极大变异
+        if (percent(40))
+            v += v * .04 * (nextFloat() - 0.5); // v=v+-.04
+        if (percent(10))
+            v += v * .103 * (nextFloat() - 0.5); // v=v+-0.1
+        else if (percent(5))
+            v += v * 1 * (nextFloat() - 0.5); // v=v+-0.4
+        else if (percent(2))
+            v += v * 4 * (nextFloat() - 0.5); // v=v+-2
+        else if (percent(1f))
+            v += v * 8 * (nextFloat() - 0.5); // v=v+-6
+        return v;
+    }
+
+    public static int varyInLimit(int v, int from, int to) {// 让返回值在from和to之间随机变异
+        int i = vary(v);
+        if (i < from)
+            i = from;
+        if (i > to)
+            i = to;
+        return i;
+    }
+
+    public static float varyInLimit(float v, float from, float to) {// 让返回值在from和to之间随机变异
+        float i = vary(v);
+        if (i < from)
+            i = from;
+        if (i > to)
+            i = to;
+        return i;
+    }
+
+}