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Competition Arena > LuckyXor

LuckyXor

SRM 665 · 2015-06-30 · by tehqin

SRM 665 · 2015-06-30 · by tehqin · Simple Math
Class Name: LuckyXor
Return Type: int
Method Name: construct
Arg Types: (int)
Problem Statement

Problem Statement

A lucky number is a positive integer consisting of only the digits 4 and 7.


Given an int a, return an int b strictly greater than a, such that a XOR b is a lucky number. (See Notes for the definition of XOR.) The number b should be in the range 1 to 100, inclusive. If such a number does not exist, return -1. If there are multiple such b, you may return any of them.

Notes

  • XOR is the bitwise exclusive-or operation. To compute the value of P XOR Q, we first write P and Q in binary. Then, each bit of the result is computed by applying XOR to the corresponding bits of the two numbers, using the rules 0 XOR 0 = 0, 0 XOR 1 = 1, 1 XOR 0 = 1, and 1 XOR 1 = 0.
  • For example, let's compute 21 XOR 6. In binary these two numbers are 10101 and 00110, hence their XOR is 10011 in binary, which is 19 in decimal.
  • You can read more about the XOR operation here: https://en.wikipedia.org/wiki/Exclusive_or

Constraints

  • a is between 1 and 100, inclusive.
Examples
0)
4
Returns: 40

4 XOR 40 = 44, 44 is a lucky number.

1)
19
Returns: 20

19 XOR 20 = 7

2)
88
Returns: 92

88 XOR 92 = 4

3)
36
Returns: -1
4)
1
Returns: 5

Submissions are judged against all 30 archived test cases, of which 5 are shown here. Case numbers match the judge’s.

Coding Area

Language: C++17 · define a public class LuckyXor with a public method int construct(int a) · 30 test cases · 2 s / 256 MB per case

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