add new solutions

solutions/0/q84/solution.go

@@ -0,0 +1,29 @@
+package q84
+
+func largestRectangleArea(heights []int) int {
+	var largest int
+	st := make([][2]int, 0, 256) // x index, height
+
+	for x, h := range heights {
+		minX := x
+		for len(st) > 0 && st[len(st)-1][1] > h {
+			largest = max(largest, st[len(st)-1][1]*(x-st[len(st)-1][0]))
+			minX = min(minX, st[len(st)-1][0])
+			st = st[:len(st)-1]
+		}
+
+		if len(st) > 0 && st[len(st)-1][1] == h {
+			continue
+		}
+		st = append(st, [2]int{minX, h})
+	}
+
+	for i := range st {
+		x, h := st[i][0], st[i][1]
+		largest = max(largest, h*(len(heights)-x))
+	}
+
+	return largest
+}
+
+var _ = largestRectangleArea