feat: solve No.513

Author: BaffinLee

Diff for: 501-600/513. Find Bottom Left Tree Value.md

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+# 513. Find Bottom Left Tree Value
+
+- Difficulty: Medium.
+- Related Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree.
+- Similar Questions: .
+
+## Problem
+
+Given the `root` of a binary tree, return the leftmost value in the last row of the tree.
+
+ 
+Example 1:
+
+![](https://assets.leetcode.com/uploads/2020/12/14/tree1.jpg)
+
+```
+Input: root = [2,1,3]
+Output: 1
+```
+
+Example 2:
+
+![](https://assets.leetcode.com/uploads/2020/12/14/tree2.jpg)
+
+```
+Input: root = [1,2,3,4,null,5,6,null,null,7]
+Output: 7
+```
+
+ 
+**Constraints:**
+
+
+	
+- The number of nodes in the tree is in the range `[1, 104]`.
+	
+- `-231 <= Node.val <= 231 - 1`
+
+
+
+## Solution
+
+```javascript
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var findBottomLeftValue = function(root) {
+    return dfs(root, 0)[0];
+};
+
+var dfs = function(node, depth) {
+    var left = node.left ? dfs(node.left, depth + 1) : [node.val, depth];
+    var right = node.right ? dfs(node.right, depth + 1) : [node.val, depth];
+    return right[1] > left[1] ? right : left;
+};
+```
+
+**Explain:**
+
+nope.
+
+**Complexity:**
+
+* Time complexity : O(n).
+* Space complexity : O(1).