# Computing the sum of integers from 1 to N

suggest changeThe following method computes the sum of integers from 0 to N using recursion.

public int sum(final int n) { if (n > 0) { return n + sum(n - 1); } else { return n; } }

This method is O(N) and can be reduced to a simple loop using tail-call optimization. In fact there is a *closed form* expression that computes the sum in `O(1)`

operations.

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