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  1. #include <iostream>
  2.  
  3.  
  4. unsigned long long getClosestWith7(unsigned long long n, unsigned int k)
  5. {
  6.     // Count number of digits
  7.     unsigned long long tmp = n;
  8.     unsigned int m = 0, mK = 0;
  9.     while(tmp > 0)
  10.     {
  11.         if(tmp % 10 == 7) mK++;
  12.         tmp /= 10;
  13.         m++;
  14.     }
  15.  
  16.     // Distinct cases
  17.     if(k == mK && n != 0)
  18.         return n;
  19.     else if(k >= m || n == 0) // implicit: k != mK
  20.     {
  21.         unsigned long long r = 0;
  22.         while(k > 0)
  23.         {
  24.             r = 10 * r + 7;
  25.             k--;
  26.         }
  27.         return r;
  28.     }
  29.     else if(k > mK) // implicit: k != mK, k < m
  30.     {
  31.         unsigned long long r = n;
  32.         unsigned long long s = 0;
  33.         m = 0;
  34.         while(mK < k)
  35.         {
  36.             if(r % 10 != 7) mK++;
  37.             r /= 10;
  38.             m++;
  39.         }
  40.         if(r % 10 == 8) // special case
  41.             s = 79 + 100 * (r / 10);
  42.         while(m > 0)
  43.         {
  44.             r = 10 * r + 7;
  45.             if(s != 0 && m > 1) // special case
  46.                 s = 10 * s + 7;
  47.             m--;
  48.         }
  49.         return (r < n && n - r < n - s) || (r >= n && r - n < n - s) ? r : s;
  50.     }
  51.     else // implicit : k < mK
  52.     {
  53.         // Generate a and b
  54.         unsigned long long a = n;
  55.         unsigned long long b = 0;
  56.         m = 0;
  57.         while(mK > k)
  58.         {
  59.             if(a % 10 == 7) mK--;
  60.             a /= 10;
  61.             m++;
  62.         }
  63.         b = 10 * a + 8;
  64.         a = 10 * a + 6;
  65.         m--;
  66.         while(m > 0)
  67.         {
  68.             a = 10 * a + 9;
  69.             b = 10 * b + 0;
  70.             m--;
  71.         }
  72.  
  73.         // Compare (return lowest if equal)
  74.         return n - a <= b - n ? a : b;
  75.     }
  76. }
  77.  
  78. #define CLOSEST7( N , K ) \
  79.     std::cout << "N = " << N << ", K = " << K << " => N' = " << getClosestWith7(N,K) << "\n"
  80.  
  81. int main()
  82. {
  83.     CLOSEST7(1773,3);
  84.     CLOSEST7(83,1);
  85.     CLOSEST7(17273,3);
  86.     CLOSEST7(1273679750,6);
  87.     CLOSEST7(1773,1);
  88.     CLOSEST7(83,5);
  89.     CLOSEST7(0,2);
  90.     CLOSEST7(0,0);
  91. }
Success #stdin #stdout 0s 2856KB
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N = 1773, K = 3 => N' = 1777
N = 83, K = 1 => N' = 79
N = 17273, K = 3 => N' = 17277
N = 1273679750, K = 6 => N' = 1273677777
N = 1773, K = 1 => N' = 1769
N = 83, K = 5 => N' = 77777
N = 0, K = 2 => N' = 77
N = 0, K = 0 => N' = 0
https://ideone.com/8eevEa
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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