Added counting sort (OmkarPathak#27)

* Added counting sort

* Longest Decreasing Subsequence

Author: Ankit-555

Dynamic Programming/LongestDecreasingSubsequence.py

@@ -0,0 +1,27 @@
+def lds(arr, n): 
+  
+    lds = [0] * n 
+    max = 0
+  
+    # Initialize LDS with 1 for all index 
+    # The minimum LDS starting with any 
+    # element is always 1 
+    for i in range(n): 
+        lds[i] = 1
+  
+    # Compute LDS from every index 
+    # in bottom up manner 
+    for i in range(1, n): 
+        for j in range(i): 
+            if (arr[i] < arr[j] and 
+                lds[i] < lds[j] + 1): 
+                lds[i] = lds[j] + 1
+  
+    # Select the maximum  
+    # of all the LDS values 
+    for i in range(n): 
+        if (max < lds[i]): 
+            max = lds[i] 
+  
+    # returns the length of the LDS 
+    return max

Sorting/Counting_sort.py

@@ -0,0 +1,32 @@
+def countSort(arr): 
+  
+    # The output character array that will have sorted arr 
+    output = [0 for i in range(256)] 
+  
+    # Create a count array to store count of inidividul 
+    # characters and initialize count array as 0 
+    count = [0 for i in range(256)] 
+  
+    # For storing the resulting answer since the  
+    # string is immutable 
+    ans = ["" for _ in arr] 
+  
+    # Store count of each character 
+    for i in arr: 
+        count[ord(i)] += 1
+  
+    # Change count[i] so that count[i] now contains actual 
+    # position of this character in output array 
+    for i in range(256): 
+        count[i] += count[i-1] 
+  
+    # Build the output character array 
+    for i in range(len(arr)): 
+        output[count[ord(arr[i])]-1] = arr[i] 
+        count[ord(arr[i])] -= 1
+  
+    # Copy the output array to arr, so that arr now 
+    # contains sorted characters 
+    for i in range(len(arr)): 
+        ans[i] = output[i] 
+    return ans