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7. Reverse Integer

Problem Statement

Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-2^31, 2^31 - 1], then return 0.

Assume the environment does not allow you to store 64-bit integers (signed or unsigned).

Solution

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int reverse(int x) {
    int ans = 0;

    while (x) {
        if (ans > INT_MAX / 10 || ans < INT_MIN / 10)
            return 0;
        ans = ans * 10 + x % 10;
        x /= 10;
    }

    return ans;
}
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