Question

I am doing a problem of spoj i tried to do it but I am always getting TLE(time limit expired )
the question is Hotels . this is my code , please can you tell me the way to optimize it.

#include<stdio.h>

int main()
{
    unsigned long long int a,b,i;
    scanf("%llu %llu",&a,&b);
    unsigned long long int arr[a];
    for(i=0;i<a;i++)
    {
        scanf("%llu",&arr[i]);
    }


        unsigned long long int d;
        unsigned long long int k,z=0;
    for(i=0;i<a;i++)
    {
        d = arr[i];
        for(k=i+1;k<a+1;k++)
        {
            if (d<b)
            {
                if(z<d)
                z = d;
            }
            else
            if(d==b)
            {
                z = d;
                break;
            }
            else
            break;
            d = d + arr[k];
        }
        if(d==b)
        break;
    }
    printf("%llu",z);
    return 0;
}

in this like if input 5 12 , these five are 2 1 3 4 5 to make 12 then i do like this :
first i compare 12 with 2 , then 2+1 , then 2+1+3 and so on after it goes to 5 it compares 12 to 1 , 1+3 , 1+3+4 .. and in this way i am taking only consecutive and break when i find equal to 12 otherwise it goes on till last.

Hitesh

Answer 1

There is no need to restart again as you said in the explanation after it goes to 5 it compares 12 to 1 , 1+3 , 1+3+4 .. and in this way. Look at your approach carefully, you are recalculating the sums of a subarray again and again. For e.g – You have already calculated sum of subarray 1+3+4 when you were doing 2+1+3+4. Hence there is still some scope of optimization.

Before telling the exact solution, I want you to try it out first. Also as one more hint refer to the following problem Find subarray with given sum.

EDIT: Sharing complete solution for future purpose.

#include<stdio.h>

/* Returns the maximum possible sum less than or equal to the gieven sum */
int subArraySum(int arr[], int n, int sum)
{
    /* Initialize curr_sum as value of first element
     and starting point as 0 */
    int curr_sum = arr[0], max_sum = 0, start = 0, i;

    /* Add elements one by one to curr_sum and if the curr_sum exceeds the
     sum, then remove starting element */
    for (i = 1; i <= n; i++)
    {
        // If curr_sum exceeds the sum, then remove the starting elements
        while (curr_sum > sum && start < i-1)
        {
            curr_sum = curr_sum - arr[start];
            start++;
        }

        //keep track of the maximum sum so far.
        if (max_sum < curr_sum)
            max_sum = curr_sum;

        curr_sum = curr_sum + arr[i];
    }

    return max_sum;
}

// Driver program to test above function

int main()
{
    int arr[] = {7, 3, 5, 6};
    int n = sizeof(arr)/sizeof(arr[0]);
    int sum = 9;
    printf("Max Sum = %d\n", subArraySum(arr, n, sum));
    return 0;
}