This is a demo task.
An 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] = 1P = 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:
class Solution { public int solution(int[] A); }
that, given an 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.
Write an efficient algorithm for the following assumptions:
- 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].
// you can also use imports, for example:
// import java.math.*;
class Test {
public int equi ( int[] A ) {
int sum = arraySum(A);
if(sum == 0) return 0;
else{
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i;
}
return -1;
}
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
./Solution.java:3: duplicate class: Test class Test { ^ wrapper.java:26: cannot access Solution bad class file: RegularFileObject[./Solution.java] file does not contain class Solution Please remove or make sure it appears in the correct subdirectory of the classpath. Solution sol = new Solution(); ^ 2 errors
// you can also use imports, for example:
// import java.math.*;
class Solution {
public int equi ( int[] A ) {
int sum = arraySum(A);
if(sum == 0) return 0;
else{
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i;
}
return -1;
}
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
Test from the task description
got 0, but it is not equilibrium point, left sum (empty set)=0, sum[1..6]=7
// you can also use imports, for example:
// import java.math.*;
class Solution {
public int equi ( int[] A ) {
int sum = arraySum(A);
if(sum == 0) return -1;
else{
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i;
}
return -1;
}
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
Test from the task description
got -1, but equilibrium point exists, for example on position 3
// you can also use imports, for example:
// import java.math.*;
class Solution {
public int equi ( int[] A ) {
int sum = arraySum(A);
if(sum == 0) return 0;
else{
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i;
}
return -1;
}
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
Test from the task description
got 0, but it is not equilibrium point, left sum (empty set)=0, sum[1..6]=7
// you can also use imports, for example:
// import java.math.*;
class Solution {
public int equi ( int[] A ) {
int sum = arraySum(A);
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i;
}
return -1;
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
Test from the task description
got 5, but it is not equilibrium point, sum[0..4]=-3, sum[6..6]=0
// you can also use imports, for example:
// import java.math.*;
class Solution {
public int equi ( int[] A ) {
int sum = arraySum(A);
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i+1;
}
return -1;
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
// you can also use imports, for example:
// import java.math.*;
class Solution {
public int equi ( int[] A ) {
int sum = arraySum(A);
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i+1;
}
return -1;
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
// you can also use imports, for example:
// import java.math.*;
class Solution {
public int equi ( int[] A ) {
int sum = arraySum(A);
int left = 0;
for(int i=0;i<A.length;i++){
left += A[i];
sum -= A[i];
if(left == sum) return i+1;
}
return -1;
}
public int arraySum(int[] A){
int sum=0;
for(int i=0;i<A.length;i++){
sum+=A[i];
}
return sum;
}
}
The following issues have been detected: wrong answers.
Sequence with extremly large numbers testing arithmetic overflow.
got 2, but it is not equilibrium point, sum[0..1]=4294967294, sum[3..3]=-2
Sequence with extremly large numbers testing arithmetic overflow.
got -1, but equilibrium point exists, for example on position 0
arithmetic overflow tests
got 1, but it is not equilibrium point, sum[0..0]=0, sum[2..2]=-2147483648
arithmetic overflow tests
got 1, but it is not equilibrium point, sum[0..0]=-2147483648, sum[2..2]=0
one large number at the end of the sequence
got -1, but equilibrium point exists, for example on position 0
multiple runs, all combinations of {-1,0,1}^2
got 1, but it is not equilibrium point, sum[0..0]=-1, right sum (empty set)=0
multiple runs, all combinations of {-1,0,1}^3
got -1, but equilibrium point exists, for example on position 1
got -1, but equilibrium point exists, for example on position 50000
got -1, but equilibrium point exists, for example on position 50002
Large performance test, O(n^2) solutions should fail.
got -1, but equilibrium point exists, for example on position 898