O(1) method

Earlier method used Dynamic Arrays to check for palindrome which took O(n) space. This method just reverses the input number and checks if it is the same as the original.

challenge_13/c/karanchawla/challenge_13.c

@@ -4,81 +4,17 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-// Dynamic Array Definition
-//////////////////////////////////////////////////////////////////////////////////
-typedef struct {
-    int *array;
-    size_t used;
-    size_t size;
-} Array;
-
-void initArray(Array *a, size_t initialSize) 
-{
-    a->array = (int *)malloc(initialSize * sizeof(int));
-    a->used = 0;
-    a->size = initialSize;
-}
-
-void insertArray(Array *a, int element) 
+int reverse(int x)
 {
-// a->used is the number of used entries, because a->array[a->used++] updates a->used only *after* the array has been accessed.
-// Therefore a->used can go up to a->size 
-    if (a->used == a->size) 
+    int ans = 0;
+    while(x != 0)
     {
-        a->size *= 2;
-        a->array = (int *)realloc(a->array, a->size * sizeof(int));
+        ans = ans * 10;
+        ans = ans + x%10;
+        x = x/10;
     }
-    a->array[a->used++] = element;
-}
-
-void freeArray(Array *a) 
-{
-    free(a->array);
-    a->array = NULL;
-    a->used = a->size = 0;
-}
-/*
-Array a;
-int i;
-initArray(&a, 5);  // initially 5 elements
-for (i = 0; i < 100; i++)
-insertArray(&a, i);  // automatically resizes as necessary
-printf("%d\n", a.array[9]);  // print 10th element
-printf("%d\n", a.used);  // print number of elements
-freeArray(&a);
-*/
-///////////////////////////////////////////////////////////////////////////////////
-
-void isPalindrome(int num)
-{
-    Array a;
-    initArray(&a,1);
-    while(num)
-    {
-        insertArray(&a, num%10);
-        num /= 10;
-    }
-
-    int size = a.used;
-
-    int flag = 1;
-    for(int i=0;i<size/2;i++)
-    {
-        if(a.array[i]==a.array[size-i-1])
-        {
-            flag = 1;
-        }
-        else 
-        {
-            flag = 0;
-            break;
-        }
-    }
-
-    if(flag) printf("True\n");
-    else printf("False\n");
-
-    freeArray(&a);
+
+    return ans;
 }
 
 
@@ -87,7 +23,14 @@ int main(void)
 {
     int num = 1234554321;
 
-    isPalindrome(num);
+    if(reverse(num)==num)
+    {
+        printf("True");
+    }
+    else
+    {
+        printf("False");
+    }
 
     return 0;
-}
+}