Minimum Depth of Binary Tree

最新推荐文章于 2023-12-15 03:22:29 发布

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最新推荐文章于 2023-12-15 03:22:29 发布

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分类专栏： leetcode Tree Depth-first Search

本文链接：https://blog.youkuaiyun.com/wang424313682/article/details/52566332

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本文介绍了解决二叉树最短深度问题的两种算法：深度优先搜索(DFS)和广度优先搜索(BFS)。通过递归方式实现DFS算法，而BFS则采用层级遍历的方法来找到从根节点到最近叶子节点的最短路径。

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Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

求二叉树的最短深度

解法一：深度优先遍历DFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int minDepth(TreeNode root) {
          if (root == null) {
			return 0;
		}
        int l = minDepth(root.left);
        int r = minDepth(root.right); 
        if (l == 0 && r == 0) return 1;
        if (l == 0 ) {
			l = Integer.MAX_VALUE;
		}
        if (r == 0) {
			r= Integer.MAX_VALUE;
		}
        
        return Math.min(l, r)+1;
    }
}

解法一：广度优先遍历BFS

public class Solution {
    public int minDepth(TreeNode root) {
          if (root == null) {
			return 0;
		}
        LinkedList<TreeNode> currLevel =  new LinkedList<TreeNode>();
       currLevel.add(root);
       int count = 1;
       while (!currLevel.isEmpty()) {
    	LinkedList<TreeNode> nextlevel = new LinkedList<TreeNode>();
		while (!currLevel.isEmpty()) {
			TreeNode node = currLevel.poll();
			if (node.left == null && node.right == null) return count;
			if (node.left != null) nextlevel.add(node.left);
			if (node.right != null) nextlevel.add(node.right);
		}
		 count++;
		 currLevel = nextlevel;
       }
       return count;
    }
}