The given `myPow` function is an implementation of a recursive...

July 2, 2025 at 04:30 PM

class Solution { public: double myPow(double x, int n) { if(x==1 || n==0){ return 1; } if(n==1){ return x; } if(n<0){ return 1/myPow(x,-n); } if(n%2==0){ return myPow(x,n/2); } else{ return x*myPow(x,n-1); } } }; what is the problem in it

The given myPow function is an implementation of a recursive algorithm to calculate (x^n) (x raised to the power n). Here is an explanation of what the code does and a potential issue:

Code Explanation:

  1. Base Cases:

    • If (x = 1) or (n = 0), the result is (1) because any number raised to the power of 0 is 1, and 1 raised to any power is 1.
    • If (n = 1), the function directly returns (x) because any number to the power of 1 is itself.
  2. Handling Negative Powers:

    • If (n < 0), the function computes the reciprocal of (x^n) (i.e., (1 / x^{-n})).
    • Note that the absolute value of (n) ((-n)) is passed recursively.
  3. Recursive Case for Even (n):

    • If (n) is even ((n % 2 == 0)), the function reduces the problem by computing (x^{n/2}) instead of multiplying (x) (n) times. This optimization reduces the work to logarithmic levels.
  4. Recursive Case for Odd (n):

    • If (n) is odd, the function computes (x) times (x^{n-1}) recursively.

This algorithm reduces the complexity to (O(\log n)), which is efficient compared to a naive (O(n)) approach.


Problem in the Code:

  1. Integer Overflow for n with Large Negative Values:

    • If (n = \text{INT_MIN}) (the smallest possible 32-bit integer, -2,147,483,648), the expression (-n) will cause an integer overflow because (-(-2,147,483,648)) is (2,147,483,648), which cannot be stored in a 32-bit signed integer.
    • This will lead to undefined behavior or incorrect results.

    Fix for this issue: Before negating (n), you can handle the case when (n = \text{INT_MIN}) explicitly:

    if (n < 0) {
        if (n == INT_MIN) {
            return 1 / (myPow(x, INT_MAX) * x);
        }
        return 1 / myPow(x, -n);
    }
    
  2. Precision Issues for Large (n):

    • For very large (n), repeated multiplications (even optimized) can result in floating-point precision errors.

Correctness in Edge Cases:

To ensure the code works well for all cases:

  • Explicitly handle cases like (x = 0, n < 0) (division by zero error).
  • Handle (n = \text{INT_MIN}) as described above.
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