513.Find Bottom Left Tree Value

Posted on | In

Tree, Medium

Question

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

Example 1:

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Input:
    2
   / \
  1   3
Output:
1

Example 2: 

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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.

Answer

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

Time complexity: O(n)