Fitcher-yates algo and Algo to find equilibrium index

Author: kumar91gopi

EquilibriumIndexofArray.rb

@@ -0,0 +1,28 @@
+=begin
+Equilibrium index of an array is an index such that the sum of elements at lower indexes is equal to the sum of elements at higher indexes.
+For example, in an arrya A:
+A[]=[-7,1,5,2,-4,3,0]
+3 is an equilibrium index, because:
+A[0] + A[1] + A[2] = A[4] + A[5] + A[6]
+Time-complexity: O(n)
+Auxiliary-space: O(1)
+=end
+
+def find_equilibrium(a)
+  len = a.length
+  leftsum=0
+  rightsum=0
+  for x in a
+    rightsum+=x
+  end
+  for i in 0...len
+    rightsum-=a[i]
+    if (leftsum == rightsum)
+      return i
+    end
+    leftsum+=a[i]
+  end
+  
+  return -1
+      
+end

FitcherYatesShufflingAlgorithm.rb

@@ -0,0 +1,20 @@
+#Fitcher-Yates shuffling algorithm
+#(start from last element,swap with random element from the array,decrement array size by one and repeat until array size is 1)
+#Time-complexity: O(n)
+
+def shuffle(arr)
+   n=arr.length
+   for i in (n-1).downto(1)
+    j=Random.rand(i+1)
+    swap(arr,i,j)
+   end
+   print arr
+end
+
+def swap(arr,i,j)
+  temp = arr[i]
+  arr[i] = arr[j]
+  arr[j] = temp
+end
+
+shuffle([1,2,3,4,5,6])

README.md

@@ -30,13 +30,16 @@ The solutions are easy to understand and complete.
 1. [Juggling Algorithm for array rotation](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/JugglingAlgorithm.rb)
 2. [Reversal Algorithm for array rotation](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/ReversalAlgorithm.rb)
 3. Block Swap Algorithm for array rotation
-    a. [Recursive](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/BlockSwapAlgorithmRecursive.rb)
-    b. [Iterative](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/BlockSwapAlgorithmIterative.rb)
+    a.[Recursive](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/BlockSwapAlgorithmRecursive.rb)
+    b.[Iterative](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/BlockSwapAlgorithmIterative.rb)
 4. [Algorithm to find maximum continuos sum in an array](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/MaxSliceSumAlgorithm.rb)
 5. [Find missing number in array](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/FindMissingNumber.rb)
 6. [Swapping two numbers](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/SwappingTwoNumbers.rb)
-7. [Shuffling an Array(Knuth Algorithm)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/KnuthShufflingAlgorithm.rb)
+7. Shuffling an Array
+    a.[Knuth shuffling Algorithm)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/KnuthShufflingAlgorithm.rb)
+    b.[Fitcher-Yates shuffling Algorithm)](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/FitcherYatesShufflingAlgorithm.rb)
 8. [Find pair in array with sum equal to given sum](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/ChekPairWithGivenSum.rb)
+9. [Find equilibrium index in an array](https://github.com/kumar91gopi/Algorithms-and-Data-Structures-in-Ruby/blob/master/EquilibriumIndexofArray.rb)