Merge pull request #887 from bus710/week06

[bus710] Week 06

Author: bus710

valid-parentheses/bus710.go

@@ -0,0 +1,55 @@
+package hello
+
+import (
+	"strings"
+)
+
+const (
+	openChar  = "({["
+	closeChar = ")]}"
+)
+
+func isValid(s string) bool {
+	ss := strings.Split(s, "")
+	stack := []string{}
+
+	// If the very first one is not an opening character,
+	// no need to check followings
+	if !strings.Contains(openChar, ss[0]) || !strings.Contains(closeChar, ss[len(ss)-1]) {
+		return false
+	}
+
+	// If the length is not even, there is an incomplete pair
+	if len(ss)%2 == 1 {
+		return false
+	}
+
+	// Loop over the slice to check
+	// - If the current one is an opening one, then push into the stack
+	// - If the current one is a closing one, then pop and compare with the previous one from the stack
+	for _, c := range ss {
+		if strings.Contains(openChar, c) {
+			stack = append(stack, c)
+		} else if strings.Contains(closeChar, c) {
+			if len(stack) == 0 {
+				return false
+			}
+			prev := stack[len(stack)-1]
+
+			switch {
+			case prev == "(" && c == ")":
+				fallthrough
+			case prev == "[" && c == "]":
+				fallthrough
+			case prev == "{" && c == "}":
+				stack = stack[:len(stack)-1]
+			default:
+				stack = append(stack, c)
+			}
+		} else {
+			// In case of non-parenthesis character found
+			return false
+		}
+	}
+	return len(stack) == 0
+}