144. 二叉树的前序遍历

Author: liuxiangyang

144. 二叉树的前序遍历.js

@@ -0,0 +1,47 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[]}
+ */
+// 递归
+var preorderTraversal = function (root) {
+  let result = []
+  let preorderTraversalNode = node => {
+    if (node) {
+      result.push(node.val)
+      preorderTraversalNode(node.left)
+      preorderTraversalNode(node.right)
+    }
+  }
+  preorderTraversalNode(root)
+  return result
+};
+
+// 递归(es6优化版本) 时间98% 空间100%
+var preorderTraversal = function (root) {
+  return root ?
+    [root.val, ...preorderTraversal(root.left),
+    ...preorderTraversal(root.right)]
+    : []
+};
+
+// 迭代
+var preorderTraversal = function (root) {
+  let result = [], stack = [], cur
+  if (root) stack.push(root)
+  while (stack.length > 0) {
+    cur = stack.pop()
+    result.push(cur.val)
+    cur.right !== null && stack.push(cur.right)
+    cur.left !== null && stack.push(cur.left)
+  }
+  return result
+};
+
+var root = [1, null, 2, 3]