LeetCode Find Bottom Left Tree Value

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

Example 1:

Input:2/ \1   3Output:
1

Example 2: 

Input:1/ \2   3/   / \4   5   6/7Output:
7

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

题解：此题比较简单，是用来求一棵二叉树中最底层中最左边那个节点的值。我考虑先求出这棵树的树高，用递归算法来求解，得到树高后，再层次遍历，遍历到树高的那一层时，直接将最左边的那个节点输出即可。

public class findBottomLeftValue
{public int findBottomLeftValue(TreeNode root){int depth = getMaxDepth(root);if(depth == 1)return root.val;Queue<TreeNode> queue = new LinkedList<>();    //层次遍历queue.add(root);int length = queue.size();int height = 1;int result = 0;while(!queue.isEmpty()){boolean t = false;while(length-- > 0){TreeNode tmp = queue.poll();if(height == depth){result = tmp.val;t = true;break;}if(tmp.left != null)queue.add(tmp.left);if(tmp.right != null)queue.add(tmp.right);}if(t == true)break;       //判断是不是最底层的最左边的那个节点height += 1;length = queue.size();}return result;}public int getMaxDepth(TreeNode root)     //递归求树高{if(root == null)return 0;else{int left = getMaxDepth(root.left);int right = getMaxDepth(root.right);return 1 + Math.max(left,right);}}
}

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