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.
代码如下：
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution { public int minDepth(TreeNode root) { Stack<Integer> stack=new Stack<>();
int depth=0;
if(root==null)
return 0; if(root.left==null&&root.right==null)
{return 1;} if(root.left!=null)
{
depth=1+minDepth(root.left);
if(stack.empty()||stack.peek()>depth)
stack.push(depth);
} if(root.right!=null)
{
depth=1+minDepth(root.right);
if(stack.empty()||stack.peek()>depth)
stack.push(depth);
} return stack.peek();
}
}