add LC_102

yi-yun · yi-yun · commit 118f45c03e1f · 2019-06-17T15:22:27.000+08:00
diff --git a/.idea/compiler.xml b/.idea/compiler.xml
diff --git a/java_test/src/main/java/com/yiyun/TestCollections.java b/java_test/src/main/java/com/yiyun/TestCollections.java
@@ -0,0 +1,18 @@
+package com.yiyun;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Collections;
+
+public class TestCollections {
+    @Test
+    public void fun(){
+        ArrayList<Integer> list = new ArrayList<>();
+        list.add(1);
+        list.add(2);
+        list.add(3);
+        list.add(4);
+        Collections.reverse(list);
+    }
+}
diff --git a/myoffer/src/main/java/leetcode/LC_102.java b/myoffer/src/main/java/leetcode/LC_102.java
@@ -0,0 +1,34 @@
+package leetcode;
+
+import org.junit.Test;
+
+import java.util.*;
+
+public class LC_102 {
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        List<List<Integer>> result = new ArrayList<>();
+        if (root==null)return result;
+        Queue<TreeNode> queue = new LinkedList<>();
+        queue.offer(root);
+        while (queue.size()>0){
+            ArrayList<Integer> list = new ArrayList<>();
+            int size = queue.size();
+            for (int i = 0; i < size; i++) {
+                TreeNode node = queue.poll();
+                list.add(node.val);
+                if (node.left!=null)queue.offer(node.left);
+                if (node.right!=null)queue.offer(node.right);
+            }
+            result.add(list);
+        }
+        Collections.reverse(result);
+        return result;
+    }
+    @Test
+    public void fun(){
+        TreeNode treeNode = new TreeNode(3, new TreeNode(9),
+            new TreeNode(20, new TreeNode(15), new TreeNode(7)));
+        List<List<Integer>> levelOrder = levelOrder(treeNode);
+        
+    }
+}
