Merge pull request gzc426#14 from Syuan-Cheng/Syuan-Cheng-patch-10

syuancheng · web-flow · commit af117e71143b · 2018-12-04T19:14:52.000+08:00
Create syuan.md
diff --git a/2018.12.04-leetcode101/syuan.md b/2018.12.04-leetcode101/syuan.md
@@ -0,0 +1,65 @@
+##### 题目
+
+```
+给定一个二叉树，检查它是否是镜像对称的。
+
+例如，二叉树 [1,2,2,3,4,4,3] 是对称的。
+
+    1
+   / \
+  2   2
+ / \ / \
+3  4 4  3
+
+但是下面这个 [1,2,2,null,3,null,3] 则不是镜像对称的:
+
+    1
+   / \
+  2   2
+   \   \
+   3    3
+```
+##### 代码
+递归
+```
+public boolean isSymmetric(TreeNode root) {
+        if (root==null) {
+            return true;
+        }else{
+            return isSymmetric(root.left,root.right);
+        }
+    }
+
+    public boolean isSymmetricCore(TreeNode leftNode, TreeNode rightNode){
+        if (leftNode==null && rightNode==null) {
+            return true;
+        }
+        if (leftNode.val!=rightNode.val || leftNode==null || rightNode==null) {
+            return false;
+        }
+        return isSymmetricCore(leftNode.left,rightNode.right) && isSymmetricCore(leftNode.right,rightNode.left);
+    }
+```
+##### 非递归法
+
+```
+class Solution {
+    public boolean isSymmetric(TreeNode root) {
+        if(root == null) return true;
+        Stack<TreeNode> stack = new Stack<TreeNode>();
+        stack.push(root.left);
+        stack.push(root.right);
+        while(!stack.empty()) {
+            TreeNode right = stack.pop();
+            TreeNode left = stack.pop();
+            if (left == null && right == null) continue;
+            else if (left == null || right == null || right.val != left.val) return false;
+            stack.push(left.left);
+            stack.push(right.right);
+            stack.push(left.right);
+            stack.push(right.left);
+        }
+        return true;
+    }
+}
+```
