add Kotlin solution for 678. Valid Parenthesis String

Author: technophilist

kotlin/0678-valid-parenthesis-string.kt

@@ -0,0 +1,57 @@
+class Solution {
+
+    fun checkValidString(s: String): Boolean {
+        // number of opening parenthesis when '*' is taken as '('
+        var noOfOpenParenthesisWhenStarIsAnOpeningParenthesis = 0
+        // number of opening parenthesis when '*' is taken as ')'
+        var noOfOpenParenthesisWhenStarIsAClosingParenthesis = 0
+        // number of opening parenthesis when '*' is taken as ' '
+        var noOfOpenParenthesisWhenStarIsAnEmptyString = 0
+
+        for (char in s) {
+            if (char == '(') {
+                noOfOpenParenthesisWhenStarIsAnOpeningParenthesis++
+                noOfOpenParenthesisWhenStarIsAClosingParenthesis++
+                noOfOpenParenthesisWhenStarIsAnEmptyString++
+
+            }
+            if (char == '*') {
+                noOfOpenParenthesisWhenStarIsAnOpeningParenthesis++
+                noOfOpenParenthesisWhenStarIsAClosingParenthesis--
+            }
+
+            if (char == ')') {
+                noOfOpenParenthesisWhenStarIsAnOpeningParenthesis--
+                noOfOpenParenthesisWhenStarIsAClosingParenthesis--
+                noOfOpenParenthesisWhenStarIsAnEmptyString--
+            }
+            // A negative value indicates an excess of closing parenthesis.
+            // Eg: -1 indicates that there are no opening parenthesis and 1 closing parenthesis.
+            // If at least one of our possibilities is a positive value, then it indicates
+            // that the string is possibly valid.
+            // If all of our possibilities have a negative value, it indicates that none of the
+            // possibilities lead to a valid string. Hence, return false.
+            if (
+                noOfOpenParenthesisWhenStarIsAnOpeningParenthesis < 0 &&
+                noOfOpenParenthesisWhenStarIsAClosingParenthesis < 0 &&
+                noOfOpenParenthesisWhenStarIsAnEmptyString < 0
+            ) return false
+
+            // Ensure that the variables are always positive. A negative value doesn't make sense
+            // because there cannot be a negative number of opening parenthesis.
+            noOfOpenParenthesisWhenStarIsAnOpeningParenthesis =
+                noOfOpenParenthesisWhenStarIsAnOpeningParenthesis.coerceAtLeast(0)
+
+            noOfOpenParenthesisWhenStarIsAClosingParenthesis =
+                noOfOpenParenthesisWhenStarIsAClosingParenthesis.coerceAtLeast(0)
+
+            noOfOpenParenthesisWhenStarIsAnEmptyString =
+                noOfOpenParenthesisWhenStarIsAnEmptyString.coerceAtLeast(0)
+
+        }
+
+        return noOfOpenParenthesisWhenStarIsAnOpeningParenthesis == 0 ||
+                noOfOpenParenthesisWhenStarIsAClosingParenthesis == 0 ||
+                noOfOpenParenthesisWhenStarIsAnEmptyString == 0
+    }
+}