public void MinDepthTest_Null()
        {
            var solution = new _111_MinimumDepthOfBinaryTree();
            var result   = solution.MinDepth(null);

            Assert.AreEqual(0, result);
        }
        public void MinDepthTest_1Layer()
        {
            var solution = new _111_MinimumDepthOfBinaryTree();
            var result   = solution.MinDepth(TestHelper.GenerateTree(new int?[] { 1 }));

            Assert.AreEqual(1, result);
        }
        public void MinDepthTest_3Layer()
        {
            var solution = new _111_MinimumDepthOfBinaryTree();
            var result   = solution.MinDepth(TestHelper.GenerateTree(new int?[] { 3, 9, 20, null, null, 15, 7 }));

            Assert.AreEqual(2, result);
        }