Add problem 678 - Valid Parenthesis Substring

Author: anirudhology

problems/greedy/valid_parenthesis_string.go

@@ -0,0 +1,38 @@
+package greedy
+
+func ValidParenthesisString(s string) bool {
+	// Minimum and maximum count of open parentheses
+	minOpen, maxOpen := 0, 0
+	// Traverse through the string
+	for _, c := range s {
+
+		if c == '(' {
+			// If it is a left parenthesis, it means you have one
+			// more open parenthesis to worry about
+			minOpen++
+			maxOpen++
+		} else if c == ')' {
+			// If it is right parenthesis, it means you have one
+			// less open parenthesis to worry about
+			minOpen--
+			maxOpen--
+		} else if c == '*' {
+			// If it is *, it means there are three cases
+			// 1. If we make it as ), then we have one less open parenthesis to worry about
+			// 2. If we make it as (, then we have one more open parentheses
+			// to worry about
+			// 3. No impact at all
+			minOpen--
+			maxOpen++
+		}
+
+		// There are more closing parentheses, then opening ones
+		if maxOpen < 0 {
+			return false
+		}
+
+		// We can't have negative open parenthesis count
+		minOpen = max(minOpen, 0)
+	}
+	return minOpen == 0
+}

tests/greedy/valid_parenthesis_string_test.go

@@ -0,0 +1,59 @@
+package greedy_test
+
+import (
+	"testing"
+
+	"github.com/anirudhology/leetcode-go/problems/greedy"
+)
+
+func TestCheckValidString(t *testing.T) {
+	// Test null input
+	if !greedy.ValidParenthesisString("") {
+		t.Errorf("Expected true for empty string")
+	}
+
+	// Test valid strings
+	if !greedy.ValidParenthesisString("()") {
+		t.Errorf("Expected true for ()")
+	}
+	if !greedy.ValidParenthesisString("(*)") {
+		t.Errorf("Expected true for (*)")
+	}
+	if !greedy.ValidParenthesisString("(*))") {
+		t.Errorf("Expected true for (*))")
+	}
+
+	// Test invalid strings
+	if greedy.ValidParenthesisString(")") {
+		t.Errorf("Expected false for )")
+	}
+	if greedy.ValidParenthesisString(")(") {
+		t.Errorf("Expected false for )(")
+	}
+	if !greedy.ValidParenthesisString("((*)") {
+		t.Errorf("Expected false for ((*)")
+	}
+	if greedy.ValidParenthesisString("((*))(") {
+		t.Errorf("Expected false for ((*))(")
+	}
+}
+
+func TestEdgeCases(t *testing.T) {
+	// Test string with only one *
+	if !greedy.ValidParenthesisString("*") {
+		t.Errorf("Expected true for *")
+	}
+
+	// Test string with multiple *
+	if !greedy.ValidParenthesisString("***") {
+		t.Errorf("Expected true for ***")
+	}
+
+	// Test strings with nested parentheses
+	if !greedy.ValidParenthesisString("(())") {
+		t.Errorf("Expected true for (())")
+	}
+	if greedy.ValidParenthesisString("(()))") {
+		t.Errorf("Expected false for (()))")
+	}
+}