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Question

A zero-indexed array A consisting of N integers is given. An equilibrium index of this array is any integer P such that 0 ≤ P < N and the sum of elements of lower indices is equal to the sum of elements of higher indices, i.e.
A[0] + A[1] + ... + A[P−1] = A[P+1] + ... + A[N−2] + A[N−1].
Sum of zero elements is assumed to be equal to 0. This can happen if P = 0 or if P = N−1.

For example, consider the following array A consisting of N = 8 elements:

A[0] = -1
A[1] = 3
A[2] = -4
A[3] = 5
A[4] = 1
A[5] = -6
A[6] = 2
A[7] = 1
P = 1 is an equilibrium index of this array, because:

A[0] = −1 = A[2] + A[3] + A[4] + A[5] + A[6] + A[7]
P = 3 is an equilibrium index of this array, because:

A[0] + A[1] + A[2] = −2 = A[4] + A[5] + A[6] + A[7]
P = 7 is also an equilibrium index, because:

A[0] + A[1] + A[2] + A[3] + A[4] + A[5] + A[6] = 0
and there are no elements with indices greater than 7.

P = 8 is not an equilibrium index, because it does not fulfill the condition 0 ≤ P < N.

Write a function:

int solution(vector<int> &A);

that, given a zero-indexed array A consisting of N integers, returns any of its equilibrium indices. The function should return −1 if no equilibrium index exists.

For example, given array A shown above, the function may return 1, 3 or 7, as explained above.

Assume that:

N is an integer within the range [0..100,000];
each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
Complexity:

expected worst-case time complexity is O(N);
expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.

Answer 1

@rishabh your code is awesome.
@mkhwanazi you can even run same code in java by replacining cout function with System.out.print and worst case time complexity of code is O(N^2)

Answer 2

@rishabh please accept java challenges

Answer 3

for(int i=1;i<n;i++)
{
int lhs=0;
int p=i;
int x=n-1;
while(p>0)
{
lhs+=A[p];
p--;
}
while(x>i)
{
lhs-=A[x];
x--;
}
if(lhs==0)
{
cout<<"Equilibrium index : "<<i<<endl;
}
}
Don't know about the complexity but still it would work.
You could define this inside a function if you like.

Answer 4

This is c++

Answer 5

No problem, kindly please mark my answer with a tick ✓ if it helped you :)
And Happy coding...

Answer 6

@vaibhav
i m glad you liked my code.
And it have not learned java much anyway if you could give me through the challenges, it would be beneficial for me.

Answer 7

which language is this?

Answer 8

Thanks man