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[leetcode]maximum depth of binary tree

admin 11月 12, 2020 0

题目描述

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

代码

可以用DFS方法

public class {
    
    public int maxDepth(TreeNode root) {
        if(root == null) return 0;
        return Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;
    }
}

也可以用BFS

public class {
    //BFS，每个节点都会进队列一次，节点出队列时统计即可
    public int maxDepth1(TreeNode root) {
      if(root == null) return 0;

      Queue<TreeNode> queue = new LinkedList<>();

      queue.offer(root);
      int level = 0;
      while(!queue.isEmpty()){
          level++;

          int size = queue.size();
          for (int i = 0; i < size; i++) {
             TreeNode node = queue.poll();
              if(node.left != null){
                  queue.offer(node.left);
              }
              if(node.right != null){
                  queue.offer(node.right);
              }
          }
      }
      return level;
    }
}