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  1. import java.math.BigInteger;
  2.  
  3. class NthRoot {
  4. 	public static void main (String[] args) {
  5. 		example(7, "100001232101001010120320");
  6. 	}
  7. 	private static void example(int n, String xstr) {
  8. 		BigInteger x = new BigInteger(xstr);
  9. 	    BigInteger y = root(n, x);
  10. 	    BigInteger z = y.pow(n);
  11. 	    BigInteger y1 = y.add(BigInteger.ONE);
  12. 	    BigInteger z1 = y1.pow(n);
  13. 		System.out.println("floor(" + x + "^(1/" + n + ")) = " + y);
  14. 		System.out.println(y + "^" + n + " = " + z);
  15. 		System.out.println(y1 + "^" + n + " = " + z1);
  16. 		System.out.println();
  17. 	}
  18. 	private static BigInteger root(int n, BigInteger x) {
  19. 		BigInteger y = BigInteger.ZERO;
  20. 		for (int m = (x.bitLength() - 1)/n; m >= 0; --m) {
  21. 			BigInteger z = y.setBit(m);
  22. 			int cmp = z.pow(n).compareTo(x);
  23. 			if (cmp == 0) return z; // found exact root
  24. 			if (cmp < 0) y = z;     // keep bit set
  25. 		}
  26. 		return y; // return floor of exact root
  27. 	}
  28. }
Success #stdin #stdout 0.11s 320512KB
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stdout
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floor(100001232101001010120320^(1/7)) = 1930
1930^7 = 99747303260050570000000
1931^7 = 100109643878654613881411
https://ideone.com/yTyk6M
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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