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.

题目含义：获得二叉树的最小高度

方法一：dfs

 1     private int findMinDepth(TreeNode node)
 2     {
 3         if (node == null) return 0;
 4         if (node.left == null&&node.right==null) return 1;
 5         
 6         if (node.left == null) return findMinDepth(node.right)+1;
 7         else if (node.right == null) return findMinDepth(node.left)+1;
 8         else return 1+Math.min(findMinDepth(node.left),findMinDepth(node.right));
 9     }
10     
11     public int minDepth(TreeNode root) {
12         if (root == null) return 0;
13         return findMinDepth(root);        
14     }
15 }

方法二：BFS

 1     public int minDepth(TreeNode root) {
 2         if (root == null) return 0;
 3         Queue<TreeNode> queue = new LinkedList<>();
 4         queue.add(root);
 5         int depth = 1;
 6         while (!queue.isEmpty())
 7         {
 8             int size = queue.size();
 9             for (int i=0;i<size;i++)
10             {
11                 TreeNode node = queue.poll();
12                 if (node.left==null && node.right==null) return depth;
13                 if (node.left !=null) queue.offer(node.left);
14                 if (node.right !=null) queue.offer(node.right);
15             }
16             depth++;
17         }
18         return depth;
19         
20     }