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fix(pow-x-n): correctness bug — JavaScript iterative solution returns wrong answer for n = INT_MIN #6044

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fix(pow-x-n): correctness bug — JavaScript iterative solution returns wrong answer for n = INT_MIN #6044

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6 changes: 4 additions & 2 deletions articles/pow-x-n.md
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Original file line number Diff line number Diff line change
Expand Up @@ -618,11 +618,11 @@ class Solution {
let power = Math.abs(n);

while (power > 0) {
if (power & 1) {
if (power % 2 === 1) {
res *= x;
}
x *= x;
power >>= 1;
power = Math.floor(power / 2);
}

return n >= 0 ? res : 1 / res;
Expand Down Expand Up @@ -773,6 +773,8 @@ impl Solution {

When `n` is `Integer.MIN_VALUE` (-2147483648), computing `abs(n)` or `-n` overflows because the positive equivalent exceeds `Integer.MAX_VALUE`. Always cast to a `long` before taking the absolute value to avoid this undefined behavior.

In JavaScript, `Math.abs(n)` is safe on its own (numbers are doubles), but the bitwise operators are not: `power & 1` and `power >>= 1` first convert `power` to a signed 32-bit integer, so `2147483648` becomes `-2147483648` and the loop terminates immediately. Use `power % 2` and `Math.floor(power / 2)` instead of bitwise operations.

### Forgetting to Handle Negative Exponents

A negative exponent means the result is `1 / x^|n|`. Omitting this reciprocal step returns the wrong answer for all negative `n` values. Compute the power using the absolute value, then invert if `n` was negative.
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