6.7 二叉树的最小深度

111. 二叉树的最小深度

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int minDepth(TreeNode root) {
        if (root == null){
            return 0;
        }
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        int min = 0;
        while (!q.isEmpty()){
            int size = q.size();
            min++;
            for (int i = 0; i < size; i++) {
                TreeNode temp = q.poll();
                if (temp.left != null) q.offer(temp.left);
                if (temp.right != null) q.offer(temp.right);
                if (temp.left == null && temp.right == null){
                    return min;
                }
            }
        }
        return min;
    }
}

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int minDepth(TreeNode root){
        //终止条件
        if (root == null) return 0;
        int left = minDepth(root.left);
        int right = minDepth(root.right);
        这里要先判断左子树/右子树是否为null
        if (root.left == null && root.right != null) return right+1;
        if (root.left!= null && root.right == null) return left + 1;
        return 1+Math.min(left,right);
    }
}