MinimumDepthofBinaryTree.java

package easy;

import util.TreeNode;
/**
 * 
 * ClassName: MinimumDepthofBinaryTree
 * @author chenyiAlone  
 * Create Time: 2019/01/10 20:52:39
 * Description: No.111
 * 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.
    
    Note: A leaf is a node with no children.
    
    Example:
    
    Given binary tree [3,9,20,null,null,15,7],
    
        3
       / \
      9  20
        /  \
       15   7
    return its minimum depth = 2.
 */
public class MinimumDepthofBinaryTree {
    public int minDepth(TreeNode root) {
        return minRec(root);
    }
    public static int minRec(TreeNode root) {
        if (root == null) return 0; 
        if (root.left != null && root.right != null)return 1 + Math.min(minRec(root.left), minRec(root.right));
        else if (root.left == null) return 1 + minRec(root.right);
        else return 1 + minRec(root.left);
    }
}