Here is a simple program test task, it doesn't have very diffcult logic:
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 = 7 elements:
A[0] = -7 A[1] = 1 A[2] = 5 A[3] = 2 A[4] = -4 A[5] = 3 A[6] = 0
P = 3 is an equilibrium index of this array, because:
- A[0] + A[1] + A[2] = A[4] + A[5] + A[6]
P = 6 is also an equilibrium index, because:
- A[0] + A[1] + A[2] + A[3] + A[4] + A[5] = 0
and there are no elements with indices greater than 6.
P = 7 is not an equilibrium index, because it does not fulfill the condition 0 ≤ P < N.
Write a function
class Solution { int solution(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.
Assume that:
- N is an integer within the range [0..10,000,000];
- each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
For example, given array A such that
A[0] = -7 A[1] = 1 A[2] = 5 A[3] = 2 A[4] = -4 A[5] = 3 A[6] = 0
the function may return 3 or 6, as explained above.
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.
At very beginning, I have wrotten down this:
// 62 of 100 using System; // you can also use other imports, for example: // using System.Collections.Generic; class Solution { public int solution(int[] A) { if(A.Length <=1) return -1; //abc int sumA = 0; foreach(int i in A){ sumA += i; } int j = 0; int tempSum = A[0]; for(j = 1; j<A.Length; j++){ //A[0] + A[1] + ... + A[P−1] = A[P+1] + ... + A[N−2] + A[N−1]. //return P if(sumA - tempSum - A[j] == tempSum){ break; } tempSum += A[j]; } if (j == A.Length || j == A.Length - 1) return -1; else return j; } }
I got 62 points of 100. because it missed border check and one misunderstanding.
So I updated it to this one:
//100 of 100 using System; // you can also use other imports, for example: // using System.Collections.Generic; class Solution { public int solution(int[] A) { //N is an integer within the range [0..10,000,000]; if(A.Length <1 || A.Length >10000000) return -1; //single number if(A.Length == 1) return 0; //each element of array A is an integer within the range [−2,147,483,648..2,147,483,647] Int64 sumA = 0; foreach(int i in A){ sumA += i; } int j = 0; //each element of array A is an integer within the range [−2,147,483,648..2,147,483,647] Int64 tempSum = 0; for(; j<A.Length; j++){ //A[0] + A[1] + ... + A[P−1] = A[P+1] + ... + A[N−2] + A[N−1]. //return P if(sumA - tempSum - A[j] == tempSum){ break; } tempSum += A[j]; } //P = 7 is not an equilibrium index, because it does not fulfill the condition 0 ≤ P < N if (j == A.Length) return -1; else return j; } }
Now, I got 100 points.
This task is from a test website.