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score: 12 of 100

 1. equiFind an index in an array such that its prefix sum equals its suffix sum.

Task description This is a demo task. You can read about this task and its solutions in this blog post. A zero-indexed array A consisting of N integers is given. Anequilibrium 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 { public int equi(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. Copyright 2009–2013 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.

Solution Time Elapsed: 29 min. (?) Notes:   not defined yet Task timeline Use the controls below to see how the code changed during the test.       17:17:47 17:01:34 Code: 17:17:47 UTC, java, final, score: 11.76 01.// you can also use imports, for example: 02.// import java.math.*; 03.class Solution { 04.public int equi ( int[] A ) { 05.int sum = arraySum(A); 06.int left = 0; 07.for(int i=0;i<A.length;i++){ 08.left += A[i]; 09.sum -= A[i]; 10.if(left == sum) return i+1; 11.} 12.return -1; 13.} 14.public int arraySum(int[] A){ 15.int sum=0; 16.for(int i=0;i<A.length;i++){ 17.sum+=A[i]; 18.} 19.return sum; 20.} 21.  22.} Analysis test time result example Test from the task description 0.308 s. OK simple 0.304 s. WRONG ANSWER got 3, but it is not equilibrium point, sum[0..2]=6, sum[4..5]=3 extreme_large_numbers Sequence with extremly large numbers testing arithmetic overflow. 0.296 s. WRONG ANSWER got 2, but it is not equilibrium point, sum[0..1]=4294967294, sum[3..3]=-2 extreme_negative_numbers Sequence with extremly large numbers testing arithmetic overflow. 0.312 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 0 overflow_tests1 arithmetic overflow tests 0.304 s. WRONG ANSWER got 1, but it is not equilibrium point, sum[0..0]=0, sum[2..2]=-2147483648 overflow_tests2 arithmetic overflow tests 0.304 s. WRONG ANSWER got 1, but it is not equilibrium point, sum[0..0]=-2147483648, sum[2..2]=0 one_large one large number at the end of the sequence 0.300 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 0 sum_0 sequence with sum=0 0.296 s. WRONG ANSWER got 3, which is not valid array index single single number 0.304 s. WRONG ANSWER got 1, which is not valid array index empty Empty array 0.300 s. OK combinations_of_two multiple runs, all combinations of {-1,0,1}^2 0.308 s. WRONG ANSWER got 1, but it is not equilibrium point, sum[0..0]=-1, right sum (empty set)=0 combinations_of_three multiple runs, all combinations of {-1,0,1}^3 0.304 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 1 small_pyramid 0.304 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 42 large_long_sequence_of_ones 0.320 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 50000 large_long_sequence_of_minus_ones 0.324 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 50002 medium_pyramid 0.320 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 402 large_pyramid Large performance test, O(n^2) solutions should fail. 0.352 s. WRONG ANSWER got -1, but equilibrium point exists, for example on position 898