/* random.c Compute random numbers within given ranges */ /* Copyright 2003-2020 by Steven S. Skiena; all rights reserved. Permission is granted for use in non-commerical applications provided this copyright notice remains intact and unchanged. These programs appear in my books: "The Algorithm Design Manual" by Steven Skiena, second edition, Springer, London 2008. See out website www.algorist.com for additional information or https://www.amazon.com/exec/obidos/ASIN/1848000693/thealgorith01-20 "Programming Challenges: The Programming Contest Training Manual" by Steven Skiena and Miguel Revilla, Springer-Verlag, New York 2003. See our website www.programming-challenges.com for additional information, or https://www.amazon.com/exec/obidos/ASIN/0387001638/thealgorithmrepo/ */ #include #include #include #include "random.h" /**************************************************************************/ /* These functions generate random numbers in the designated ranges */ void swap(int *a, int *b) { int x; x = *a; *a = *b; *b = x; } int random_int(int low, int high) { /* lower/upper bounds on numb*/ int i, j, r; /* random number*/ i = RAND_MAX / (high - low + 1); i *= (high - low + 1); while ((j = rand()) >= i) { continue; } r = (j % (high - low + 1)) + low; if ((r < low) || (r > high)) { printf("Error: random integer %d out of range [%d,%d]\n", r, low, high); } return(r); } /* Construct a random permutation of the \$n\$ elements of the given array. */ void random_permutation(int a[], int n) { int i; for (i=n; i>1; i--) { swap(&a[i - 1], &a[random_int(0, i - 1)]); } } double random_float(int low, int high) { /*lower/upper bounds on numb*/ double i, j; /* avoid arithmetic trouble */ double r; /* random number*/ i = RAND_MAX / (high - low); i *= (high - low); while ((j = rand()) >= i) { continue; } r = (j / i) * (high - low) + low; if ((r < low) || (r > high)) { printf("ERROR: random real %f out of range [%d,%d]\n", r, low, high); } return(r); }