Task: Fraction reduction
C: #include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct IntArray_t {
    int *ptr;
    size_t length;
} IntArray;

IntArray make(size_t size) {
    IntArray temp;
    temp.ptr = calloc(size, sizeof(int));
    temp.length = size;
    return temp;
}

void destroy(IntArray *ia) {
    if (ia->ptr != NULL) {
        free(ia->ptr);

        ia->ptr = NULL;
        ia->length = 0;
    }
}

void zeroFill(IntArray dst) {
    memset(dst.ptr, 0, dst.length * sizeof(int));
}

int indexOf(const int n, const IntArray ia) {
    size_t i;
    for (i = 0; i < ia.length; i++) {
        if (ia.ptr[i] == n) {
            return i;
        }
    }
    return -1;
}

bool getDigits(int n, int le, IntArray digits) {
    while (n > 0) {
        int r = n % 10;
        if (r == 0 || indexOf(r, digits) >= 0) {
            return false;
        }
        le--;
        digits.ptr[le] = r;
        n /= 10;
    }
    return true;
}

int removeDigit(IntArray digits, size_t le, size_t idx) {
    static const int POWS[] = { 1, 10, 100, 1000, 10000 };
    int sum = 0;
    int pow = POWS[le - 2];
    size_t i;
    for (i = 0; i < le; i++) {
        if (i == idx) continue;
        sum += digits.ptr[i] * pow;
        pow /= 10;
    }
    return sum;
}

int main() {
    int lims[4][2] = { { 12, 97 }, { 123, 986 }, { 1234, 9875 }, { 12345, 98764 } };
    int count[5] = { 0 };
    int omitted[5][10] = { {0} };
    size_t upperBound = sizeof(lims) / sizeof(lims[0]);
    size_t i;

    for (i = 0; i < upperBound; i++) {
        IntArray nDigits = make(i + 2);
        IntArray dDigits = make(i + 2);
        int n;

        for (n = lims[i][0]; n <= lims[i][1]; n++) {
            int d;
            bool nOk;

            zeroFill(nDigits);
            nOk = getDigits(n, i + 2, nDigits);
            if (!nOk) {
                continue;
            }
            for (d = n + 1; d <= lims[i][1] + 1; d++) {
                size_t nix;
                bool dOk;

                zeroFill(dDigits);
                dOk = getDigits(d, i + 2, dDigits);
                if (!dOk) {
                    continue;
                }
                for (nix = 0; nix < nDigits.length; nix++) {
                    int digit = nDigits.ptr[nix];
                    int dix = indexOf(digit, dDigits);
                    if (dix >= 0) {
                        int rn = removeDigit(nDigits, i + 2, nix);
                        int rd = removeDigit(dDigits, i + 2, dix);
                        if ((double)n / d == (double)rn / rd) {
                            count[i]++;
                            omitted[i][digit]++;
                            if (count[i] <= 12) {
                                printf("%d/%d = %d/%d by omitting %d's\n", n, d, rn, rd, digit);
                            }
                        }
                    }
                }
            }
        }

        printf("\n");

        destroy(&nDigits);
        destroy(&dDigits);
    }

    for (i = 2; i <= 5; i++) {
        int j;

        printf("There are %d %d-digit fractions of which:\n", count[i - 2], i);

        for (j = 1; j <= 9; j++) {
            if (omitted[i - 2][j] == 0) {
                continue;
            }
            printf("%6d have %d's omitted\n", omitted[i - 2][j], j);
        }

        printf("\n");
    }

    return 0;
}

Python: def indexOf(haystack, needle):
    idx = 0
    for straw in haystack:
        if straw == needle:
            return idx
        else:
            idx += 1
    return -1

def getDigits(n, le, digits):
    while n > 0:
        r = n % 10
        if r == 0 or indexOf(digits, r) >= 0:
            return False
        le -= 1
        digits[le] = r
        n = int(n / 10)
    return True

def removeDigit(digits, le, idx):
    pows = [1, 10, 100, 1000, 10000]
    sum = 0
    pow = pows[le - 2]
    i = 0
    while i < le:
        if i == idx:
            i += 1
            continue
        sum = sum + digits[i] * pow
        pow = int(pow / 10)
        i += 1
    return sum

def main():
    lims = [ [ 12, 97 ], [ 123, 986 ], [ 1234, 9875 ], [ 12345, 98764 ] ]
    count = [0 for i in range(5)]
    omitted = [[0 for i in range(10)] for j in range(5)]

    i = 0
    while i < len(lims):
        n = lims[i][0]
        while n < lims[i][1]:
            nDigits = [0 for k in range(i + 2)]
            nOk = getDigits(n, i + 2, nDigits)
            if not nOk:
                n += 1
                continue
            d = n + 1
            while d <= lims[i][1] + 1:
                dDigits = [0 for k in range(i + 2)]
                dOk = getDigits(d, i + 2, dDigits)
                if not dOk:
                    d += 1
                    continue
                nix = 0
                while nix < len(nDigits):
                    digit = nDigits[nix]
                    dix = indexOf(dDigits, digit)
                    if dix >= 0:
                        rn = removeDigit(nDigits, i + 2, nix)
                        rd = removeDigit(dDigits, i + 2, dix)
                        if (1.0 * n / d) == (1.0 * rn / rd):
                            count[i] += 1
                            omitted[i][digit] += 1
                            if count[i] <= 12:
                                print "%d/%d = %d/%d by omitting %d's" % (n, d, rn, rd, digit)
                    nix += 1
                d += 1
            n += 1
        print
        i += 1

    i = 2
    while i <= 5:
        print "There are %d %d-digit fractions of which:" % (count[i - 2], i)
        j = 1
        while j <= 9:
            if omitted[i - 2][j] == 0:
                j += 1
                continue
            print "%6s have %d's omitted" % (omitted[i - 2][j], j)
            j += 1
        print
        i += 1
    return None

main()