【LeetCode】513.Find Bottom Left Tree Value(Medium)解题报告

【LeetCode】513.Find Bottom Left Tree Value(Medium)解题报告

题目地址：https://leetcode.com/problems/find-bottom-left-tree-value/description/

题目描述：

  Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:
Input:

2
/ \
1   3

Output:
1
Example 2:
Input:

1
/ \
2   3
/   / \
4   5   6
/
7

Output:
7
Note: You may assume the tree (i.e., the given root node) is not NULL.

Solution:

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
time : O(n)
space : O(n)
*/
class Solution {
int res = 0;
int height = 0;
public int findBottomLeftValue(TreeNode root) {
if(root == null) return -1;
helper(root,1);
return res;
}
public void helper(TreeNode root, int depth){
if(root == null) return;
if(height < depth){
res = root.val;
height = depth;
}
helper(root.left , depth +1);
helper(root.right, depth +1);
}
}

Solution2：

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
time : O(n)
space : O(n)
*/
class Solution {
public int findBottomLeftValue(TreeNode root) {
if(root == null) return -1;
int res = 0;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while(!queue.isEmpty()){
TreeNode cur = queue.poll();
res = cur.val;
if(cur.right != null) queue.offer(cur.right);
if(cur.left != null) queue.offer(cur.left);
}
return res;
}
}

Date：2018年3月19日