LeetCode_111

题目

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.

题目解析

给定一棵两叉树，求树的最小深度。

实现

/** * 定义二叉树 * */class BinaryTreeNode {    int value;    BinaryTreeNode left;    BinaryTreeNode right;    public BinaryTreeNode() {    }    public BinaryTreeNode(int val) {        this.value = val;    }}public class Solution {    // 记录树的最小深度    private int min = Integer.MAX_VALUE;    // 当前处理的树的节点    private int cur = 0;    public int minDepth(BinaryTreeNode root) {        depth(root);        return min;    }    /**     * 计算树的深度     *     * @param node 当前结点     */    private void depth(BinaryTreeNode node) {        if (node == null) {            min = cur;            return;        }        cur++; // 当前处理的层次加1        // 如果是叶节点，并且路径比记录的最小还小        if (node.left == null && node.right == null && cur < min) {            min = cur; // 更新最小值        }        // 处理左子树        if (node.left != null) {            depth(node.left);        }        // 处理右子树        if (node.right != null) {            depth(node.right);        }        cur--; // 还原    }    public static void main(String[] args)    {        BinaryTreeNode root=new BinaryTreeNode(1);        BinaryTreeNode left1=new BinaryTreeNode(2);        BinaryTreeNode left2=new BinaryTreeNode(3);        BinaryTreeNode right1=new BinaryTreeNode(4);        BinaryTreeNode right2=new BinaryTreeNode(4);        //创建一棵树        root.left=left1;        left1.right=left2;        root.right=right1;       // right1.right=right2;        Solution solution = new Solution();        System.out.print(solution.minDepth(root));    }}