add kotlin solution for 901 Online-Stock-Span.kt

Author: MagicienDeCode

Diff for: May-LeetCoding-Challenge/19-Online-Stock-Span/Online-Stock-Span.kt

@@ -0,0 +1,60 @@
+import java.util.*
+
+/**
+ * Your StockSpanner object will be instantiated and called as such:
+ * var obj = StockSpanner()
+ * var param_1 = obj.next(price)
+ */
+class OnlineStockSpanKotlin901 {
+    // 100 80 60 70 60 75 85
+    // 1    1 1  2  1  4  6
+
+    // 100 1    add 100
+    // 100 1 -> 80 1    add 80
+    // 100 1 -> 80 1 -> 60 1    add 60
+    // 100 1 -> 80 1 -> 70 2    add 70
+    // 100 1 -> 80 1 -> 70 2 -> 60 1    add 60
+    // 100 1 -> 80 1 -> 75 4    add 75
+    // 100 1 -> 85 6    add 85
+
+    // 1384 ms
+    // first price, second count
+    private val priceCountStack: Stack<Pair<Int, Int>> = Stack()
+    fun next(price: Int): Int {
+        var count = 1
+        // stack peek won't remove the element, just return the reference of last added element
+        while (priceCountStack.isNotEmpty() && priceCountStack.peek().first <= price) {
+            count += priceCountStack.pop().second
+        }
+        priceCountStack.push(Pair(price, count))
+        return count
+    }
+
+    /*
+    1884 ms
+    private val prices: MutableList<Int> = ArrayList()
+    fun next(price: Int): Int {
+        var count = 1
+        loop@ for (index in prices.size - 1 downTo 0) {
+            when {
+                prices[index] <= price -> ++count
+                else -> break@loop
+            }
+        }
+        prices.add(price)
+        return count
+    }
+     */
+}
+
+fun main() {
+    val solution = OnlineStockSpanKotlin901()
+    // 1112146
+    print(solution.next(100))
+    print(solution.next(80))
+    print(solution.next(60))
+    print(solution.next(70))
+    print(solution.next(60))
+    print(solution.next(75))
+    print(solution.next(85))
+}