111. Minimum Depth of Binary Tree

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