Common basic algorithm C + + implementation

October 06, 2016 10:40:43

This article records some commonly used basic algorithms, only for practice practice , the content of the words will be indexed

Prime (prime number) judgment

The definition of prime number: that is, except for itself and 1, there are no other approximate numbers

1 BOOLIsPrime (inti)2 {3      for(intj =2;J <= sqrt (i * 1.0); J + +) {4         if(i% J = =0)5             return false;6     }7     return true;8}

Greatest common divisor

For example: for the greatest common divisor of 24 and 60, first decomposition of factorization, 24=2x2x2x3,60=2x2x3x5,24 and 60 of all the public quality factor is 2, 2, 3, their product is 2x2x3=12, so, (24,60) =12

1 intgcdintAintb//Greatest Common Divisor2 {3      return（！ b) X:GDC (y,x%y);4 }5 6 //or more easily understood.7 intgcdintAintb//Greatest Common Divisor8 {9      while(a%b) {Ten         intTMP =A; OneA =b; Ab = tmp%b; -     } -     returnb; the}

With the greatest common divisor, least common multiple is very good, expressed as a*b/greatest common divisor

Multiply by large number

The read and output of the large number are different from the normal number, and the read-in is a string that is read in, the multiplied number is deposited into the array, and then the output data of the array is traversed.

Let's take a look at the principle of multiplication.

A = B = 25

A and b multiplication process show

B 2 5

A 3 4

----------------------------------------the multiplication process, just like we do in our cognition, there is no rounding.

8 (2x4) (4X5)

6 (2X3) (3X5)

---------------------------------------------------------the normal multiplication, still not carry

6 23 20

---------------------------------------------------------can get the answers we're familiar with by rounding 850

8 5 0

(6+2 (rounding)) (3+2 (rounding)) rounding explanation

Through the above analysis, we know the core idea of the algorithm , then we can implement the algorithm, the implementation method is as follows:

1 voidMultiplyConst CharBConst Char*b) {2ASSERT (A! = NULL && b! = null!);3      intI, J, LA, LB;4La =strlen (a);5LB =strlen (b);6      intS[LA+LB] = {0};7       for(i =0; I < LA; i++) {//complete multiplication, but no rounding8           for(j =0; J < lb; J + +){9S[I+J] + = (a[i)-'0') * (b[j]-'0');Ten          } One      } A       for(i =0; i < la+lb; i++) {//Complete Rounding -s[i+1] + = s[i]/Ten; -S[i] = s[i]%Ten; the      } -       for(i = la+lb; I >=0; i-- ){ -          if(S[i]! =0) cout <<S[i]; -      } +}

Common basic algorithm C + + implementation