Cracking the coding interview: Equilibrium Point — 8

Steven Lu
1 min readJul 25, 2022


Given an array A of n positive numbers. The task is to find the first Equilibium Point in the array.
Equilibrium Point in an array is a position such that the sum of elements before it is equal to the sum of elements after it.

Note: Retun the index of Equilibrium point. (1-based index)

Example 1:

n = 5
A[] = {1,3,5,2,2}
Output: 3
For second test case
equilibrium point is at position 3
as elements before it (1+3) =
elements after it (2+2).

Example 2:

n = 1
A[] = {1}
Output: 1
Since its the only element hence
its the only equilibrium point.

Your Task:
The task is to complete the function equilibriumPoint() which takes the array and n as input parameters and returns the point of equilibrium. Return -1 if no such point exists.

Expected Time Complexity: O(n)
Expected Auxiliary Space: O(1)

1 <= n <= 106
1 <= A[i] <= 108


Time complexity: O(n)

Space complexity: O(1)



Steven Lu

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