二叉树的右视图

nibnait · Mar 20, 2020 · 3697116 · 3697116
1 parent 18349ca
commit 3697116
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diff --git a/src/main/java/algorithm_practice/LeetCode/code100/M199_二叉树的右视图.java b/src/main/java/algorithm_practice/LeetCode/code100/M199_二叉树的右视图.java
@@ -32,65 +32,68 @@ public void testCase() {
         Integer[] root = {1, 2, 3, null, 5, null, 4};
         System.out.println(rightSideView(ConstructBinaryTree.constructByBFSArray(root)));
 
-        Integer[] root1 = {1, 2, 3, null, 5, null, 4};
+        Integer[] root1 = {};
         System.out.println(rightSideView(ConstructBinaryTree.constructByBFSArray(root1)));
 
+        Integer[] root2 = {1, 2};
+        System.out.println(rightSideView(ConstructBinaryTree.constructByBFSArray(root2)));
+
+        Integer[] root3 = {1, 2, 3, 4};
+        System.out.println(rightSideView(ConstructBinaryTree.constructByBFSArray(root3)));
 
-    }
 
+    }
 
     /**
      * 1. 层先法遍历二叉树
-     * 2. 然后取第1、2、4、8、16...个结点上的val
+     * // 2. 然后取第1、2、4、8、16...个结点上的val
+     * 2. 遇到每一层的最后一个元素 记录下来。
      */
     public List<Integer> rightSideView(TreeNode root) {
-        List<Integer> bfsArray = new ArrayList<>();
-
-        bfsTravel(root, bfsArray);
-//        System.out.println(JSON.toJSONString(bfsArray));
+//        PrintBinaryTree.print(root);
 
         List<Integer> result = new ArrayList<>();
-        int row = 0;
-        int index = Double.valueOf(Math.pow(2, row)).intValue();
-        while (index <= bfsArray.size()) {
-            int rightIndex = index - 1;
-            Integer node = bfsArray.get(rightIndex);
-            if (node != null) {
-                result.add(node);
-            } else {
-                while (bfsArray.get(--rightIndex) != null) {
-                    result.add(node);
-                }
-            }
 
-            index += Double.valueOf(Math.pow(2, ++row)).intValue();
+        if (root == null) {
+            return result;
         }
 
-        return bfsArray;
-    }
-
-    private void bfsTravel(TreeNode root, List<Integer> bfsArray) {
-
-        bfsArray.add(root.val);
-
+        // queue是当前层的所有节点
         LinkedList<TreeNode> queue = new LinkedList<>();
-        queue.addLast(root.left);
-        queue.addLast(root.right);
+        // 下一层的所有节点
+        LinkedList<TreeNode> nextRowQueue = new LinkedList<>();
+
+        int val = root.val;
+        queue.add(root);
 
         while (!queue.isEmpty()) {
+            while (!queue.isEmpty()) {
+                TreeNode treeNode = queue.poll();
 
-            TreeNode treeNode = queue.pollFirst();
-            bfsArray.add(treeNode.val);
+                if (treeNode != null && treeNode.val != null) {
+                    val = treeNode.val;
+                }
 
-            if (isNotLeafNode(treeNode)) {
-                queue.addLast(treeNode.left);
-                queue.addLast(treeNode.right);
+                if (treeNode != null && !isLeafNode(treeNode)) {
+                    nextRowQueue.add(treeNode.left);
+                    nextRowQueue.add(treeNode.right);
+                }
             }
+            result.add(val);
+            copyToQueue(nextRowQueue, queue);
         }
+        return result;
+    }
 
+    private void copyToQueue(LinkedList<TreeNode> nextRowQueue, LinkedList<TreeNode> queue) {
+        queue.clear();
+        while (!nextRowQueue.isEmpty()){
+            queue.add(nextRowQueue.poll());
+        }
     }
 
-    private boolean isNotLeafNode(TreeNode treeNode) {
-        return treeNode.left != null && treeNode.right != null;
+    private boolean isLeafNode(TreeNode treeNode) {
+        return treeNode.left == null && treeNode.right == null;
     }
+
 }
diff --git a/src/main/java/common/util/ConstructBinaryTree.java b/src/main/java/common/util/ConstructBinaryTree.java
@@ -47,9 +47,12 @@ public static TreeNode constructByBFSArray(Integer[] bfsArray) {
             Integer leftValue = bfsArray[count++];
             pop.left = new TreeNode(leftValue);
             queue.add(pop.left);
-            Integer rightValue = bfsArray[count++];
-            pop.right = new TreeNode(rightValue);
-            queue.add(pop.right);
+
+            if (count + 1 <= bfsArray.length) {
+                Integer rightValue = bfsArray[count++];
+                pop.right = new TreeNode(rightValue);
+                queue.add(pop.right);
+            }
         }
         return head;
     }

diff --git a/src/main/test/Main.java b/src/main/test/Main.java
@@ -1,10 +1,12 @@
 import com.alibaba.fastjson.JSONObject;
 import com.google.common.base.Functions;
 import com.google.common.collect.Lists;
+import common.datastruct.TreeNode;
 import junit.framework.TestCase;
 import org.junit.Test;
 
 import java.util.ArrayList;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Stack;
 
@@ -15,8 +17,14 @@ public class Main extends TestCase {
 
     @Test
     public void testCase() {
-        String str = "aabcccccaa";
-        System.out.println(compressString(str));
+        LinkedList<TreeNode> queue = new LinkedList<>();
+        queue.add(null);
+        queue.add(null);
+        queue.add(null);
+        queue.add(null);
+
+        System.out.println(queue.isEmpty());
+
     }
 
     public String compressString(String S) {