Merge pull request #391 from s-sanyal/master

Added Stock-Span-Problem

data_structures/Stacks/Stock-Span-Problem.py

@@ -0,0 +1,51 @@
+'''
+The stock span problem is a financial problem where we have a series of n daily 
+price quotes for a stock and we need to calculate span of stock’s price for all n days.
+
+The span Si of the stock’s price on a given day i is defined as the maximum 
+number of consecutive days just before the given day, for which the price of the stock 
+on the current day is less than or equal to its price on the given day.
+'''
+def calculateSpan(price, S): 
+      
+    n = len(price) 
+    # Create a stack and push index of fist element to it 
+    st = []  
+    st.append(0) 
+  
+    # Span value of first element is always 1 
+    S[0] = 1 
+  
+    # Calculate span values for rest of the elements 
+    for i in range(1, n): 
+          
+        # Pop elements from stack whlie stack is not 
+        # empty and top of stack is smaller than price[i] 
+        while( len(st) > 0 and price[st[0]] <= price[i]): 
+            st.pop() 
+  
+        # If stack becomes empty, then price[i] is greater 
+        # than all elements on left of it, i.e. price[0], 
+        # price[1], ..price[i-1]. Else the price[i]  is 
+        # greater than elements after top of stack 
+        S[i] = i+1 if len(st) <= 0 else (i - st[0]) 
+  
+        # Push this element to stack 
+        st.append(i) 
+  
+  
+# A utility function to print elements of array 
+def printArray(arr, n): 
+    for i in range(0,n): 
+        print arr[i], 
+  
+  
+# Driver program to test above function 
+price = [10, 4, 5, 90, 120, 80] 
+S = [0 for i in range(len(price)+1)] 
+  
+# Fill the span values in array S[] 
+calculateSpan(price, S) 
+  
+# Print the calculated span values 
+printArray(S, len(price))