Data commit

Task/Fraction-reduction/C-sharp/fraction-reduction.cs

@@ -0,0 +1,94 @@
+using System;
+
+namespace FractionReduction {
+    class Program {
+        static int IndexOf(int n, int[] s) {
+            for (int i = 0; i < s.Length; i++) {
+                if (s[i] == n) {
+                    return i;
+                }
+            }
+            return -1;
+        }
+
+        static bool GetDigits(int n, int le, int[] digits) {
+            while (n > 0) {
+                var r = n % 10;
+                if (r == 0 || IndexOf(r, digits) >= 0) {
+                    return false;
+                }
+                le--;
+                digits[le] = r;
+                n /= 10;
+            }
+            return true;
+        }
+
+        static int RemoveDigit(int[] digits, int le, int idx) {
+            int[] pows = { 1, 10, 100, 1000, 10000 };
+
+            var sum = 0;
+            var pow = pows[le - 2];
+            for (int i = 0; i < le; i++) {
+                if (i == idx) continue;
+                sum += digits[i] * pow;
+                pow /= 10;
+
+            }
+            return sum;
+        }
+
+        static void Main() {
+            var lims = new int[,] { { 12, 97 }, { 123, 986 }, { 1234, 9875 }, { 12345, 98764 } };
+            var count = new int[5];
+            var omitted = new int[5, 10];
+            var upperBound = lims.GetLength(0);
+            for (int i = 0; i < upperBound; i++) {
+                var nDigits = new int[i + 2];
+                var dDigits = new int[i + 2];
+                var blank = new int[i + 2];
+                for (int n = lims[i, 0]; n <= lims[i, 1]; n++) {
+                    blank.CopyTo(nDigits, 0);
+                    var nOk = GetDigits(n, i + 2, nDigits);
+                    if (!nOk) {
+                        continue;
+                    }
+                    for (int d = n + 1; d <= lims[i, 1] + 1; d++) {
+                        blank.CopyTo(dDigits, 0);
+                        var dOk = GetDigits(d, i + 2, dDigits);
+                        if (!dOk) {
+                            continue;
+                        }
+                        for (int nix = 0; nix < nDigits.Length; nix++) {
+                            var digit = nDigits[nix];
+                            var dix = IndexOf(digit, dDigits);
+                            if (dix >= 0) {
+                                var rn = RemoveDigit(nDigits, i + 2, nix);
+                                var rd = RemoveDigit(dDigits, i + 2, dix);
+                                if ((double)n / d == (double)rn / rd) {
+                                    count[i]++;
+                                    omitted[i, digit]++;
+                                    if (count[i] <= 12) {
+                                        Console.WriteLine("{0}/{1} = {2}/{3} by omitting {4}'s", n, d, rn, rd, digit);
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+                Console.WriteLine();
+            }
+
+            for (int i = 2; i <= 5; i++) {
+                Console.WriteLine("There are {0} {1}-digit fractions of which:", count[i - 2], i);
+                for (int j = 1; j <= 9; j++) {
+                    if (omitted[i - 2, j] == 0) {
+                        continue;
+                    }
+                    Console.WriteLine("{0,6} have {1}'s omitted", omitted[i - 2, j], j);
+                }
+                Console.WriteLine();
+            }
+        }
+    }
+}