added simplify_fraction.js

simplify_fraction.js

@@ -0,0 +1,48 @@
+const divide = require("./divide.js");
+const is_even = require("./is_even.js");
+const min = require("./min.js");
+const primes = require("./primes.js");
+
+function simplify_fraction(numerator, denominator) {
+  // divide by prime numbers up to 1000
+  const digits = primes("2", min(["1000", denominator, denominator]));
+
+  // shave off excess zeros
+  while (numerator.endsWith("0") && denominator.endsWith("0")) {
+    numerator = numerator.substring(0, numerator.length - 1);
+    denominator = denominator.substring(0, denominator.length - 1);
+  }
+
+  while (is_even(numerator) && is_even(denominator)) {
+    numerator = divide(numerator, "2");
+    denominator = divide(denominator, "2");
+  }
+
+  let proceed = true;
+  while (proceed) {
+    proceed = false;
+
+    // attempt to divide numerator and denominator by the same digit
+    for (let i = 0; i < digits.length; i++) {
+      const digit = digits[i];
+      const digit_length = digit.length;
+      const max_decimal_digits = digit_length + 1;
+      const numerator_divided = divide(numerator, digit, { ellipsis: true, max_decimal_digits });
+      if (numerator_divided.indexOf(".") === -1) {
+        const denominator_divided = divide(denominator, digit, { ellipsis: true, max_decimal_digits });
+        if (denominator_divided.indexOf(".") === -1) {
+          // console.log(`both "${numerator} and ${denominator} are evenly divisible by "${digit}"`);
+          numerator = numerator_divided;
+          denominator = denominator_divided;
+          proceed = true;
+          break;
+        }
+      }
+    }
+  }
+
+  return [numerator, denominator];
+}
+
+module.exports = simplify_fraction;
+module.exports.default = simplify_fraction;