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addmorsvs.l157

Sum of positive integers 0 through N that are divisible by 3 or 7

Algorithms
Logic
Algebra
Mathematics

Arithmetic progression, int itself an integer number of divisions by 3, 7, 21;

Code
Diff
  • int foo(int n){
    
      return
        ((int)n/3 *(3 + n - n % 3)+
        (int)n/7 *(7 + n- n % 7) -
        (int)n/21 *(21 + n - n % 21))/2;
}
    • int foo(int n){
    • if (n < 0) {
    • return 0;
    • }
    • int count_3 = n / 3;
    • int count_7 = n / 7;
    • int count_21 = n / 21;
    • return
    • count_3 *(3 + n - n % 3) /2 +
    • count_7 *(7 + n- n % 7) / 2 -
    • count_21 *(21 + n - n % 21) /2;
    • ((int)n/3 *(3 + n - n % 3)+
    • (int)n/7 *(7 + n- n % 7) -
    • (int)n/21 *(21 + n - n % 21))/2;
    • }