Merge pull request #1198 from imrushi/leetcode-239

Create Go: solution for 239-Sliding-Window-Maximum.go and 150-Evaluate-Reverse-Polish-Notation.go

Author: Ahmad-A0

Diff for: go/150-Evaluate-Reverse-Polish-Notation.go

@@ -0,0 +1,32 @@
+func evalRPN(tokens []string) int {
+	var stack []int
+	var a, b int
+	for _, c := range tokens {
+		switch c {
+		case "+":
+			a, b, stack = getAndPopLastOperand(stack)
+			stack = append(stack, (a + b))
+		case "-":
+			a, b, stack = getAndPopLastOperand(stack)
+			stack = append(stack, (a - b))
+		case "*":
+			a, b, stack = getAndPopLastOperand(stack)
+			stack = append(stack, (a * b))
+		case "/":
+			a, b, stack = getAndPopLastOperand(stack)
+			stack = append(stack, (a / b))
+		default:
+			i, _ := strconv.Atoi(c)
+			stack = append(stack, i)
+		}
+	}
+	return stack[0]
+}
+
+func getAndPopLastOperand(stack []int) (int, int, []int) {
+	a := stack[len(stack)-2]
+	b := stack[len(stack)-1]
+	stack = stack[:len(stack)-2]
+
+	return a, b, stack
+}

Diff for: go/239-Sliding-Window-Maximum.go

@@ -0,0 +1,28 @@
+func maxSlidingWindow(nums []int, k int) []int {
+	// get top/last element of queue: q[len(q)-1]
+	// pop/remove from the top/last element of queue: q[:len(q)-1]
+	// remove left value from queue: q[1:]
+	output := []int{}
+	q := make([]int, 0)
+	l, r := 0, 0
+
+	for r < len(nums) {
+		// pop smaller values from q
+		for len(q) != 0 && nums[q[len(q)-1]] < nums[r] {
+			q = q[:len(q)-1]
+		}
+		q = append(q, r)
+
+		// remove left val from window
+		if l > q[0] {
+			q = q[1:]
+		}
+
+		if (r + 1) >= k {
+			output = append(output, nums[q[0]])
+			l++
+		}
+		r++
+	}
+	return output
+}