Updated README

data_structures/stacks/next_greater_element.py

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+from __future__ import print_function
+# Function to print element and NGE pair for all elements of list
+def printNGE(arr):
+ 
+    for i in range(0, len(arr), 1):
+ 
+        next = -1
+        for j in range(i+1, len(arr), 1):
+            if arr[i] < arr[j]:
+                next = arr[j]
+                break
+             
+        print(str(arr[i]) + " -- " + str(next))
+ 
+# Driver program to test above function
+arr = [11,13,21,3]
+printNGE(arr)