111.minimum depth of binary tree

题目链接：https://leetcode.com/problems/minimum-depth-of-binary-tree/description/

题目大意：求解二叉树的最小高度。

法一：BFS。新写一个class，承接TreeNode和当前结点高度。代码如下（耗时6ms）：

 1     static class MergeTree {
 2         TreeNode root;
 3         int depth;
 4         MergeTree(TreeNode r, int d) {
 5             root = r;
 6             depth = d;
 7         }
 8     }
 9     public int minDepth(TreeNode root) {
10         int res = Integer.MAX_VALUE;
11         if(root == null) {
12             return 0;
13         }
14         Queue<MergeTree> q = new LinkedList<MergeTree>();
15         MergeTree mT = new MergeTree(root, 1);
16         q.offer(mT);
17         while(!q.isEmpty()) {
18             MergeTree tmpT = q.poll();
19             TreeNode tmpN = tmpT.root;
20             if(tmpN.left != null) {
21                 mT = new MergeTree(tmpN.left, tmpT.depth + 1);
22                 q.offer(mT);
23             }
24             if(tmpN.right != null) {
25                 mT = new MergeTree(tmpN.right, tmpT.depth + 1);
26                 q.offer(mT);
27             }
28             if(tmpN.left == null && tmpN.right == null) {
29                 res = Math.min(res, tmpT.depth);
30             }
31         }
32         return res;
33     }

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