P17-二叉树最小深度-深度优先

//二叉树的最小深度
/*
 * 给定一个二叉树，找出其最小深度
 * 最小深度是从根节点到最近叶子节点的最短路径上的节点数量
 * */
public class P17 {
    static class TreeNode{
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode(int val, TreeNode left, TreeNode right){
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

    public static void main(String[] args) {
        TreeNode node7 = new TreeNode(7, null, null);
        TreeNode node6 = new TreeNode(6, node7, null);
        TreeNode node5 = new TreeNode(5, null, null);
        TreeNode node4 = new TreeNode(4, null, null);
        TreeNode node3 = new TreeNode(3, node6, null);
        TreeNode node2 = new TreeNode(2, node4, node5);
        TreeNode node1 = new TreeNode(1, node2, node3);
        System.out.println(minDepth(node1));
    }

    //深度优先
    public static int minDepth(TreeNode root){
        if(root == null){
            return 0;
        }

        //叶子节点，深度为1，是我们定义的
        if(root.left == null && root.right == null){
            return 1;
        }

        int min = Integer.MAX_VALUE;

        if(root.left != null){
            min = Math.min(minDepth(root.left), min);
        }
        if(root.right != null){
            min = Math.min(minDepth(root.right), min);
        }

        //左右深度+自己
        return min + 1;
    }
    
}