public void BackspaceCompareTest()
        {
            var s = new Solution();

            Assert.True(s.BackspaceCompare("ab#c", "ad#c")); // true, "ac"
            Assert.True(s.BackspaceCompare("ab##", "c#d#")); // true, ""
            Assert.True(s.BackspaceCompare("a##c", "#a#c")); // true, "c"
            Assert.False(s.BackspaceCompare("a#c", "b"));    // false, "c" > "b"
        }