LeetCode 111. Minimum Depth of Binary Tree

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.

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