Data commit

Task/Fraction-reduction/D/fraction-reduction.d

@@ -0,0 +1,91 @@
+import std.range;
+import std.stdio;
+
+int indexOf(Range, Element)(Range haystack, scope Element needle)
+if (isInputRange!Range) {
+    int idx;
+    foreach (straw; haystack) {
+        if (straw == needle) {
+            return idx;
+        }
+        idx++;
+    }
+    return -1;
+}
+
+bool getDigits(int n, int le, 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(int[] digits, int le, int idx) {
+    enum pows = [ 1, 10, 100, 1_000, 10_000 ];
+
+    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;
+}
+
+void main() {
+    auto lims = [ [ 12, 97 ], [ 123, 986 ], [ 1234, 9875 ], [ 12345, 98764 ] ];
+    int[5] count;
+    int[10][5] omitted;
+    for (int i = 0; i < lims.length; i++) {
+        auto nDigits = new int[i + 2];
+        auto dDigits = new int[i + 2];
+        for (int n = lims[i][0]; n <= lims[i][1]; n++) {
+            nDigits[] = 0;
+            bool nOk = getDigits(n, i + 2, nDigits);
+            if (!nOk) {
+                continue;
+            }
+            for (int d = n + 1; d <= lims[i][1] + 1; d++) {
+                dDigits[] = 0;
+                bool dOk = getDigits(d, i + 2, dDigits);
+                if (!dOk) {
+                    continue;
+                }
+                for (int nix = 0; nix < nDigits.length; 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 (cast(double)n / d == cast(double)rn / rd) {
+                            count[i]++;
+                            omitted[i][digit]++;
+                            if (count[i] <= 12) {
+                                writefln("%d/%d = %d/%d by omitting %d's", n, d, rn, rd, digit);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        writeln;
+    }
+
+    for (int i = 2; i <= 5; i++) {
+        writefln("There are %d %d-digit fractions of which:", count[i - 2], i);
+        for (int j = 1; j <= 9; j++) {
+            if (omitted[i - 2][j] == 0) {
+                continue;
+            }
+            writefln("%6s have %d's omitted", omitted[i - 2][j], j);
+        }
+        writeln;
+    }
+}