Task: Fraction reduction
C++: #include <array>
#include <iomanip>
#include <iostream>
#include <vector>

int indexOf(const std::vector<int> &haystack, int needle) {
    auto it = haystack.cbegin();
    auto end = haystack.cend();
    int idx = 0;
    for (; it != end; it = std::next(it)) {
        if (*it == needle) {
            return idx;
        }
        idx++;
    }
    return -1;
}

bool getDigits(int n, int le, std::vector<int> &digits) {
    while (n > 0) {
        auto r = n % 10;
        if (r == 0 || indexOf(digits, r) >= 0) {
            return false;
        }
        le--;
        digits[le] = r;
        n /= 10;
    }
    return true;
}

int removeDigit(const std::vector<int> &digits, int le, int idx) {
    static std::array<int, 5> pows = { 1, 10, 100, 1000, 10000 };

    int sum = 0;
    auto pow = pows[le - 2];
    for (int i = 0; i < le; i++) {
        if (i == idx) continue;
        sum += digits[i] * pow;
        pow /= 10;
    }
    return sum;
}

int main() {
    std::vector<std::pair<int, int>> lims = { {12, 97}, {123, 986}, {1234, 9875}, {12345, 98764} };
    std::array<int, 5> count;
    std::array<std::array<int, 10>, 5> omitted;

    std::fill(count.begin(), count.end(), 0);
    std::for_each(omitted.begin(), omitted.end(),
        [](auto &a) {
            std::fill(a.begin(), a.end(), 0);
        }
    );

    for (size_t i = 0; i < lims.size(); i++) {
        std::vector<int> nDigits(i + 2);
        std::vector<int> dDigits(i + 2);

        for (int n = lims[i].first; n <= lims[i].second; n++) {
            std::fill(nDigits.begin(), nDigits.end(), 0);
            bool nOk = getDigits(n, i + 2, nDigits);
            if (!nOk) {
                continue;
            }
            for (int d = n + 1; d <= lims[i].second + 1; d++) {
                std::fill(dDigits.begin(), dDigits.end(), 0);
                bool dOk = getDigits(d, i + 2, dDigits);
                if (!dOk) {
                    continue;
                }
                for (size_t nix = 0; nix < nDigits.size(); nix++) {
                    auto digit = nDigits[nix];
                    auto dix = indexOf(dDigits, digit);
                    if (dix >= 0) {
                        auto rn = removeDigit(nDigits, i + 2, nix);
                        auto rd = removeDigit(dDigits, i + 2, dix);
                        if ((double)n / d == (double)rn / rd) {
                            count[i]++;
                            omitted[i][digit]++;
                            if (count[i] <= 12) {
                                std::cout << n << '/' << d << " = " << rn << '/' << rd << " by omitting " << digit << "'s\n";
                            }
                        }
                    }
                }
            }
        }

        std::cout << '\n';
    }

    for (int i = 2; i <= 5; i++) {
        std::cout << "There are " << count[i - 2] << ' ' << i << "-digit fractions of which:\n";
        for (int j = 1; j <= 9; j++) {
            if (omitted[i - 2][j] == 0) {
                continue;
            }
            std::cout << std::setw(6) << omitted[i - 2][j] << " have " << j << "'s omitted\n";
        }
        std::cout << '\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()