Product of Array Except Self

First pass: set answer[i] to the product of all values before i using a running prefix initialized to one. Second pass from right to left: multiply answer[i] by a running suffix, then update the suffix with nums[i]. This naturally handles one or multiple zeroes and never divides. It runs in O(n) time and uses O(1) auxiliary space besides the required output. Updating the suffix before multiplying the answer is an off-by-one error. In an interview, make the invariant explicit before writing code, trace a boundary example that breaks a tempting shortcut, state what each stored value represents, and explain why every update preserves correctness. This verification step also surfaces empty-input, duplicate-value, and numeric-limit cases.