Recursion questions

Python/Recursion/Binary_Search.py

@@ -0,0 +1,15 @@
+def binarySearch(a,x,si,ei):
+    if si>ei:
+        return -1
+    mid = (si+ei)//2
+    if a[mid]==x:
+        return mid
+    elif a[mid]>x:
+        return binarySearch(a,x,si,mid-1)
+    else:
+        return binarySearch(a,x,mid+1,ei)
+
+a=[1,4,5,6,8,9,12,14,15,16,17,19]
+x=15
+ei = len(a)-1
+print(binarySearch(a, x, 0, ei))

Python/Recursion/Char_replace_in_string.py

@@ -0,0 +1,11 @@
+def replace(s,a,b):
+    if len(s)==0:
+        return s
+    smallOutput = replace(s[1:],a,b)
+    if s[0] == a:
+        return b + smallOutput
+    else:
+        return s[0] + smallOutput
+
+s = "bananana"
+print(replace(s,"a","b"))

Python/Recursion/CheckListSorted.py

@@ -0,0 +1,11 @@
+def isSorted(a, si):
+#     si = start index
+    l = len(a)
+    if si == l-1 or si==l:
+        return True
+    if a[si]>a[si+1]:
+        return False
+    return isSorted(a, si+1)
+
+a = [1,2,3,4,5]
+print(isSorted(a, 0))

Python/Recursion/Count_zero.py

@@ -0,0 +1,11 @@
+def count_zero(n):
+    if n == 0:
+        return 0
+
+    if n%10==0:
+        return 1 + count_zero(int(n/10))
+    else:
+        return count_zero(int(n/10))
+
+n = 405004020
+print(count_zero(n))

Python/Recursion/Factorial.py

@@ -0,0 +1,7 @@
+def fact(n):
+    if n==0:
+        return 1
+    return n * fact(n-1)
+
+n = 5
+print(fact(n))

Python/Recursion/Fibonacci_Series.py

@@ -0,0 +1,8 @@
+def fib(n):
+    if n==1 or n==2:
+        return 1
+    output = fib(n-1) + fib(n-2)
+    return output
+
+n=6
+print(fib(n))

Python/Recursion/Find_element_in_arr.py

@@ -0,0 +1,11 @@
+def findarr(a,x):
+    l = len(a)
+    if l==0:
+        return False
+    if a[0]==x:
+        return True
+    return findarr(a[1:],x)
+
+a = [1,2,3,4,5,6]
+x = 6
+print(findarr(a,x))

Python/Recursion/First_index_occurrence.py

@@ -0,0 +1,11 @@
+def firstindex(a, x, si):
+    l = len(a)
+    if si==l:
+        return -1
+    if a[si]==x:
+        return si
+    return firstindex(a,x,si+1)
+
+a = [1,4,3,7,5,4,6]
+x = 4
+print(firstindex(a, x))

Python/Recursion/Geometric_sum.py

@@ -0,0 +1,7 @@
+def geosum(k):
+    if k==0:
+        return 1
+    return (1/2**k) + geosum(k-1)
+
+k = 3
+print(geosum(k))

Python/Recursion/Last_index_occurrence.py

@@ -0,0 +1,16 @@
+def lastindex(a, x, si):
+    l = len(a)
+    if si==l:
+        return -1
+    smallerListOutput = lastindex(a, x, si+1)
+    if smallerListOutput != -1:
+        return smallerListOutput
+    else:
+        if a[si]==x:
+            return si
+        else:
+            return -1
+
+a = [1,2,4,6,7,8,4,7,6]
+x = 4
+print(lastindex(a,x,0))

Python/Recursion/Merge_sort.py

@@ -0,0 +1,39 @@
+def merge(a1,a2,a):
+    i = 0
+    j = 0
+    k = 0
+    while i<len(a1) and j<len(a2):
+        if a1[i]<a2[j]:
+            a[k] = a1[i]
+            k= k+1
+            i = i+1
+        else:
+            a[k]=a2[j]
+            k=k+1
+            j=j+1
+
+    while i<len(a1):
+        a[k] = a1[i]
+        k= k+1
+        i = i+1
+
+    while j<len(a2):
+        a[k]=a2[j]
+        k=k+1
+        j=j+1
+
+def merge_sort(a):
+    if len(a)==0 or len(a)==1:
+        return
+    mid = len(a)//2
+    a1 = a[0:mid]
+    a2 = a[mid:]
+
+    merge_sort(a1)
+    merge_sort(a2)
+
+    merge(a1,a2,a)
+
+a = [7,3,9,4,1,8,5,2,6]
+merge_sort(a)
+print(a)

Python/Recursion/Multiplication.py

@@ -0,0 +1,7 @@
+def mul(m,n):
+    if n==0:
+        return 0
+    a = mul(m,n-1)
+    return a + m
+
+print(mul(5,4))

Python/Recursion/Palindrome.py

@@ -0,0 +1,11 @@
+def palindrome(s,si,ei):
+    if si>=ei:
+        return True
+    if s[si]==s[ei]:
+        return True
+    else:
+        return False
+    palindrome(s,si+1,ei-1)
+
+s = "level"
+print(palindrome(s,0,len(s)-1))

Python/Recursion/Power.py

@@ -0,0 +1,8 @@
+def power(x,n):
+    if n==0:
+        return 1
+    return (x*power(x,n-1))
+
+x = int(input())
+n = int(input())
+print(power(x,n))

Python/Recursion/Print_1_to_n.py

@@ -0,0 +1,9 @@
+def print_1_to_n(n):
+    if n==0:
+        return
+    print_1_to_n(n-1)
+    print(n)
+    return
+
+n = 4
+print(print_1_to_n(n))

Python/Recursion/Print_n_to_1.py

@@ -0,0 +1,8 @@
+def print_n_to_1(n):
+    if n==0:
+        return
+    print(n)
+    print_n_to_1(n-1)
+
+n = 5
+print(print_n_to_1(n))

Python/Recursion/Quick_sort.py

@@ -0,0 +1,34 @@
+def partition(a,si,ei):
+    pivot = a[si]
+    c=0
+    for i in range(si,ei+1):
+        if a[i]<pivot:
+            c=c+1
+    a[si+c],a[si] = a[si],a[si+c]
+    pivot_index = si+c
+
+    i=si
+    j=ei
+
+    while i<j:
+        if a[i]<pivot:
+            i=i+1
+        elif a[j]>pivot:
+            j = j-1
+        else:
+            a[i],a[j] = a[j],a[i]
+            i=i+1
+            j=j-1
+
+    return pivot_index
+
+def quicksort(a,si,ei):
+    if si>=ei:
+        return
+    pivot_index = partition(a, si, ei)
+    quicksort(a,si,pivot_index-1)
+    quicksort(a,pivot_index+1,ei)
+
+a = [10,7,8,9,1,5]
+quicksort(a,0,len(a)-1)
+print(a)

Python/Recursion/Remove.py

@@ -0,0 +1,11 @@
+def remove(s,a):
+    if len(s)==0:
+        return s
+    smallOutput = remove(s[1:],a)
+    if s[0]==a:
+        return smallOutput
+    else:
+        return s[0] + smallOutput
+
+s = "xaxxb"
+print(remove(s, 'x'))

Python/Recursion/Rempve_duplicate.py

@@ -0,0 +1,8 @@
+def duplicate(s):
+    if len(s)==0 or len(s)==1:
+        return s
+    if s[0]==s[1]:
+        return duplicate(s[1:])
+    return s[0] + duplicate(s[1:])
+
+print(duplicate("xyxxtttzzwwa"))

Python/Recursion/Replace_pi.py

@@ -0,0 +1,13 @@
+def replacePi(s):
+    if len(s)==0 or len(s)==1:
+        return s
+
+    if s[0]=="p" and s[1]=="i":
+        smalloutput = replacePi(s[2:])
+        return "3.14" + smalloutput
+
+    else:
+        smalloutput = replacePi(s[1:])
+        return s[0] + smalloutput
+
+print(replacePi("abcpipipipppddfpi"))

Python/Recursion/String_to_integer.py

@@ -0,0 +1,11 @@
+def strtoint(s):
+    if len(s)==1:
+        return ord(s[0]) - ord('0')
+    y = strtoint(s[1:])
+    x = ord(s[0]) - ord('0')
+    x = x* (10**(len(s) - 1)) + y
+    return x
+
+s = "12345"
+print(strtoint(s))
+print(type(strtoint(s)))

Python/Recursion/Sum_of_arr.py

@@ -0,0 +1,9 @@
+def arrsum(a):
+    l = len(a)
+    if l==1:
+        return a[0]
+    else:
+        return a[0] + arrsum(a[1:])
+
+a = [9,8,9]
+print(arrsum(a))

Python/Recursion/Sum_of_given_int.py

@@ -0,0 +1,7 @@
+def sum_int(n):
+    if n==0:
+        return 0
+    return (n%10 + sum_int(int(n/10)))
+
+n =12345
+print(sum_int(n))

Python/Recursion/Sum_of_n.py

@@ -0,0 +1,7 @@
+def sum_n(n):
+    if n==0:
+        return 0
+    return n + sum_n(n-1)
+
+n = 5
+print(sum_n(n))

Python/Recursion/Tower_of_Hanoi.py

@@ -0,0 +1,13 @@
+def towerofhanoi(n,source,destination,auxiliary):
+    if n==1:
+        print(source,destination)
+        return
+    towerofhanoi(n-1,source,auxiliary,destination)
+    print(source,auxiliary)
+    towerofhanoi(n-1,auxiliary,destination,source)
+
+n = 3
+source = "a"
+auxiliary = "b"
+destination = "c"
+print(towerofhanoi(n,source,auxiliary,destination))