diff --git a/HelloHackerRank/src/test/java/com/hello/ListRemoveTest.java b/HelloHackerRank/src/test/java/com/hello/ListRemoveTest.java
new file mode 100644
index 0000000..48e60f2
--- /dev/null
+++ b/HelloHackerRank/src/test/java/com/hello/ListRemoveTest.java
@@ -0,0 +1,75 @@
+package com.hello;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * @author dingxl
+ * @date 3/16/2021 7:05 PM
+ */
+public class ListRemoveTest {
+    @Test
+    public void testListRemoveException() {
+        List<String> list = new ArrayList<String>() {{
+            add("0");
+            add("1");
+            add("2");
+            add("3");
+            add("4");
+        }};
+
+        for (int i = 0; i < list.size(); i++) {
+            if (i % 2 == 0) {
+                System.out.printf("remove: %s\n", list.get(i));
+                list.remove(i);
+            } else {
+                System.out.printf("keep: %s\n", list.get(i));
+            }
+        }
+    }
+
+    @Test
+    public void testListRemove() {
+        List<String> list = new ArrayList<String>() {{
+            add("0");
+            add("1");
+            add("2");
+            add("3");
+            add("4");
+        }};
+
+        for (int i = list.size() - 1; i >= 0; i--) {
+            if (i % 2 == 0) {
+                System.out.printf("remove: %s\n", list.get(i));
+                list.remove(i);
+            } else {
+                System.out.printf("keep: %s\n", list.get(i));
+            }
+        }
+    }
+
+    @Test
+    public void testIteratorRemove() {
+        List<String> list = new ArrayList<String>() {{
+            add("0");
+            add("1");
+            add("2");
+            add("3");
+            add("4");
+        }};
+
+        Iterator<String> it = list.iterator();
+        while (it.hasNext()) {
+            String str = it.next();
+            if (Integer.parseInt(str) % 2 == 0) {
+                System.out.printf("remove: %s\n", str);
+                it.remove();
+            } else {
+                System.out.printf("keep: %s\n", str);
+            }
+        }
+    }
+}
diff --git a/push_master.sh b/push_master.sh
new file mode 100644
index 0000000..102d2bf
--- /dev/null
+++ b/push_master.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+git checkout master
+
+git push origin master
+git push gitee master
+git push github master