From b6fc7729ff174dbce61088c960dc44dab4c97b26 Mon Sep 17 00:00:00 2001
From: Angelica Hjelm Gardner <angelica.hjelm.gardner@ericsson.com>
Date: Sun, 17 Nov 2024 23:06:01 +0100
Subject: [PATCH] feat(LeetCode #20): add Valid input Parentheses pair solution

---
 LeetCode/problem020_ValidParentheses.go      | 36 ++++++++++++++++++++
 LeetCode/problem020_ValidParentheses_test.go | 33 ++++++++++++++++++
 2 files changed, 69 insertions(+)
 create mode 100644 LeetCode/problem020_ValidParentheses.go
 create mode 100644 LeetCode/problem020_ValidParentheses_test.go

diff --git a/LeetCode/problem020_ValidParentheses.go b/LeetCode/problem020_ValidParentheses.go
new file mode 100644
index 0000000..e2ebe15
--- /dev/null
+++ b/LeetCode/problem020_ValidParentheses.go
@@ -0,0 +1,36 @@
+/*
+Problem 20. Valid Parentheses
+*/
+
+package leetcode
+
+// Time complexity:  O(n)
+// Space complexity: O(n)
+func isValid(s string) bool {
+	stack := []rune{}
+
+	bracketMap := map[rune]rune{
+		')': '(',
+		'}': '{',
+		']': '[',
+	}
+
+	for _, char := range s {
+		if char == '(' || char == '{' || char == '[' {
+			stack = append(stack, char)
+		} else {
+			if len(stack) == 0 {
+				return false
+			}
+
+			top := stack[len(stack)-1]
+			stack = stack[:len(stack)-1]
+
+			if top != bracketMap[char] {
+				return false
+			}
+		}
+	}
+
+	return len(stack) == 0
+}
diff --git a/LeetCode/problem020_ValidParentheses_test.go b/LeetCode/problem020_ValidParentheses_test.go
new file mode 100644
index 0000000..e63951d
--- /dev/null
+++ b/LeetCode/problem020_ValidParentheses_test.go
@@ -0,0 +1,33 @@
+package leetcode
+
+import (
+	"testing"
+)
+
+func TestIsValid(t *testing.T) {
+	var tests = []struct {
+		name        string
+		inputString string
+		expected    bool
+	}{
+		{"Case 1", "()", true},
+		{"Case 2", "()[]{}", true},
+		{"Case 3", "(]", false},
+		{"Case 4", "{[]}", true},
+		{"Correct and incorrect example", "{[}", false},
+		{"Empty string", "", true},
+		{"Only opening parentheses", "(", false},
+		{"Only closing parentheses", ")", false},
+		{"Longer correct example", "({[]})[]{}", true},
+		{"Longer incorrect example", "({[]})[]{}{", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isValid(tt.inputString)
+			if result != tt.expected {
+				t.Errorf("isValid(%q) = %v; expected %v", tt.inputString, result, tt.expected)
+			}
+		})
+	}
+}