Merge pull request #868 from hjwforever/patch-4

update: 0257.二叉树的所有路径, 增加go与js版本的递归解法

problems/0257.二叉树的所有路径.md

@@ -469,6 +469,9 @@ class Solution:
 ---
 
 Go：
+  
+递归法：
+  
 ```go
 func binaryTreePaths(root *TreeNode) []string {
     res := make([]string, 0)
@@ -491,10 +494,45 @@ func binaryTreePaths(root *TreeNode) []string {
     return res
 }
 ```
+  
+迭代法：
+
+```go
+func binaryTreePaths(root *TreeNode) []string {
+	stack := []*TreeNode{}
+	paths := make([]string, 0)
+	res := make([]string, 0)
+	if root != nil {
+		stack = append(stack, root)
+		paths = append(paths, "")
+	}
+	for len(stack) > 0 {
+		l := len(stack)
+		node := stack[l-1]
+		path := paths[l-1]
+		stack = stack[:l-1]
+		paths = paths[:l-1]
+		if node.Left == nil && node.Right == nil {
+			res = append(res, path+strconv.Itoa(node.Val))
+			continue
+		}
+		if node.Right != nil {
+			stack = append(stack, node.Right)
+			paths = append(paths, path+strconv.Itoa(node.Val)+"->")
+		}
+		if node.Left != nil {
+			stack = append(stack, node.Left)
+			paths = append(paths, path+strconv.Itoa(node.Val)+"->")
+		}
+	}
+	return res
+}
+```
+
 ---
 JavaScript:
 
-1.递归版本
+递归法：
 
 ```javascript
 var binaryTreePaths = function(root) {
@@ -518,6 +556,32 @@ var binaryTreePaths = function(root) {
 };
 ```
 
+迭代法：
+
+```javascript
+var binaryTreePaths = function(root) {
+  if (!root) return [];
+  const stack = [root], paths = [''], res = [];
+  while (stack.length) {
+    const node = stack.pop();
+    let path = paths.pop();
+    if (!node.left && !node.right) { // 到叶子节点终止, 添加路径到结果中
+      res.push(path + node.val);
+      continue;
+    }
+    path += node.val + '->';
+    if (node.right) { // 右节点存在
+      stack.push(node.right);
+      paths.push(path);
+    }
+    if (node.left) { // 左节点存在
+      stack.push(node.left);
+      paths.push(path);
+    }
+  }
+  return res;
+};  
+```