Minimum Depth of Binary Tree leetcode java

题目：

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.

题解：

递归解法急速判断左右两边子树哪个depth最小，要注意如果有个节点只有一边孩子时，不能返回0，要返回另外一半边的depth。

递归解法：

     public int minDepth(TreeNode root) {
         if(root == null)
             return 0;
         int minleft = minDepth(root.left);
         int minright = minDepth(root.right);
         if(minleft==0 || minright==0)
             return minleft>=minright?minleft+1:minright+1;
         return Math.min(minleft,minright)+1;
     }

非递归解法：

 1     public int minDepth(TreeNode root) {
 2         if(root == null)
 3             return 0;
 4         
 5         int depth = 1;//The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.
 6         LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
 7         queue.add(root);
 8         int curnum = 1;
 9         int nextnum = 0;
         while(!queue.isEmpty()){
             TreeNode cur = queue.poll();
             curnum--;
             
             if(cur.left == null && cur.right == null)
                 return depth;
             
             if(cur.left != null){
                queue.add(cur.left);
                nextnum++;
             }
             
             if(cur.right != null){
                 queue.add(cur.right);
                 nextnum++;
             }
             
             if(curnum == 0){
                 curnum = nextnum;
                 nextnum = 0;
                 depth++;
             }
         }
         return depth;
     }