Question

I am building an optimal binary search tree. I have its root table and main table, and i am trying to construct the binary tree from the root table. I do not know how, can you please build a program that does so? for more info, my array is 600 strings, and the frequencies are randomly chosen. Thank You! In C Please!

Answer 1

Hi,

The information you provided is not enough but I have shared with you the code of optimal BST. Hope this helps for you. You can modify this code in order to get the solution.

#include <stdio.h>

#include <limits.h>

// A utility function to get sum of array elements

// freq[i] to freq[j]

int sum(int freq[], int i, int j);

// A recursive function to calculate cost of optimal

// binary search tree

int optCost(int freq[], int i, int j)

{

   // Base cases

   if (j < i)      // no elements in this subarray

     return 0;

   if (j == i)     // one element in this subarray

     return freq[i];

   // Get sum of freq[i], freq[i+1], ... freq[j]

   int fsum = sum(freq, i, j);

   // Initialize minimum value

   int min = INT_MAX;

   // One by one consider all elements as root and

   // recursively find cost of the BST, compare the

   // cost with min and update min if needed

   for (int r = i; r <= j; ++r)

   {

       int cost = optCost(freq, i, r-1) +

                  optCost(freq, r+1, j);

       if (cost < min)

          min = cost;

   }

   // Return minimum value

   return min + fsum;

}

// The main function that calculates minimum cost of

// a Binary Search Tree. It mainly uses optCost() to

// find the optimal cost.

int optimalSearchTree(int keys[], int freq[], int n)

{

     // Here array keys[] is assumed to be sorted in

     // increasing order. If keys[] is not sorted, then

     // add code to sort keys, and rearrange freq[]

     // accordingly.

     return optCost(freq, 0, n-1);

}

// A utility function to get sum of array elements

// freq[i] to freq[j]

int sum(int freq[], int i, int j)

{

    int s = 0;

    for (int k = i; k <=j; k++)

       s += freq[k];

    return s;

}

// Driver program to test above functions

int main()

{

    int keys[] = {10, 12, 20};

    int freq[] = {34, 8, 50};

    int n = sizeof(keys)/sizeof(keys[0]);

    printf("Cost of Optimal BST is %d ",

               optimalSearchTree(keys, freq, n));

    return 0;

}