add new solutions

solutions/0/q20/solution.go

@@ -0,0 +1,32 @@
+package q20
+
+func isValid(s string) bool {
+	stack := make([]byte, 0, len(s)/2)
+
+	for i := range len(s) {
+		switch s[i] {
+		case '(', '[', '{':
+			stack = append(stack, s[i])
+		case ')':
+			if len(stack) == 0 || stack[len(stack)-1] != '(' {
+				return false
+			}
+			stack = stack[:len(stack)-1]
+
+		case ']':
+			if len(stack) == 0 || stack[len(stack)-1] != '[' {
+				return false
+			}
+			stack = stack[:len(stack)-1]
+
+		case '}':
+			if len(stack) == 0 || stack[len(stack)-1] != '{' {
+				return false
+			}
+			stack = stack[:len(stack)-1]
+		}
+	}
+	return len(stack) == 0
+}
+
+var _ = isValid