Added hard/intersecting_lines

bradhanson · bradhanson · commit c67985765a61 · 2018-07-17T07:30:08.000-04:00
diff --git a/hard/intersecting_lines.js b/hard/intersecting_lines.js
@@ -0,0 +1,89 @@
+/**
+ * Using the JavaScript language, have the function intersectingLines(strArr)
+ * take strArr which will be an array of 4 coordinates in the form: (x,y). Your
+ * program should take these points where the first 2 form a line and the last 2
+ * form a line, and determine whether the lines intersect, and if they do, at
+ * what point. For example: if strArr is ["(3,0)","(1,4)","(0,-3)","(2,3)"],
+ * then the line created by (3,0) and (1,4) and the line created by (0,-3) (2,3)
+ * intersect at (9/5,12/5). Your output should therefore be the 2 points in
+ * fraction form in the following format: (9/5,12/5). If there is no denominator
+ * for the resulting points, then the output should just be the integers like
+ * so: (12,3). If any of the resulting points is negative, add the negative sign
+ * to the numerator like so: (-491/63,-491/67). If there is no intersection,
+ * your output should return the string "no intersection". The input points and
+ * the resulting points can be positive or negative integers.
+ *
+ * https://www.coderbyte.com/results/bhanson:Intersecting%20Lines:JavaScript
+ *
+ * @param  {array} strArr
+ * @return {string}
+ */
+function intersectingLines(strArr) {
+    // https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection
+    const [x1, y1, x2, y2, x3, y3, x4, y4] = strArr
+        .join('')
+        .match(/-?\d+/g)
+        .map(Number);
+
+    // https://wikimedia.org/api/rest_v1/media/math/render/svg/c51a9b486a6ef5a7a08b92d75e71a07888034a9a
+    const pxNumerator =
+        (x1 * y2 - y1 * x2) * (x3 - x4) - (x1 - x2) * (x3 * y4 - y3 * x4);
+    const pxDenominator = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);
+
+    const pyNumerator =
+        (x1 * y2 - y1 * x2) * (y3 - y4) - (y1 - y2) * (x3 * y4 - y3 * x4);
+    const pyDenominator = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);
+
+    // The problem is solved at this point, but we need to format the answer to spec
+
+    if (pxDenominator === 0 || pyDenominator === 0) {
+        return 'no intersection';
+    }
+
+    const pxString = formatFractionToString(pxNumerator, pxDenominator);
+    const pyString = formatFractionToString(pyNumerator, pyDenominator);
+
+    return `(${pxString},${pyString})`;
+}
+
+function greatestCommonFactor(num0, num1) {
+    num0 = Math.abs(num0);
+    num1 = Math.abs(num1);
+
+    if (num0 === 0) return num1;
+    if (num1 === 0) return num0;
+
+    const max = Math.min(num0, num1);
+    let gcf = 1;
+    for (let i = 1; i <= max; i++) {
+        if (num0 % i === 0 && num1 % i === 0) {
+            gcf = i;
+        }
+    }
+    return gcf;
+}
+
+function formatFractionToString(numerator, denominator) {
+    // Reduce fraction
+    const gcf = greatestCommonFactor(numerator, denominator);
+    numerator /= gcf;
+    denominator /= gcf;
+
+    // Combine signs and remove from elements to add at end
+    sign = Math.sign(numerator) * Math.sign(denominator) === 1 ? '' : '-';
+    numerator = Math.abs(numerator);
+    denominator = Math.abs(denominator);
+
+    let str;
+    if (numerator === 0) {
+        str = '0';
+    } else if (numerator === denominator || denominator === 1) {
+        str = `${sign}${numerator}`;
+    } else {
+        str = `${sign}${numerator}/${denominator}`;
+    }
+
+    return str;
+}
+
+module.exports = intersectingLines;
diff --git a/hard/intersecting_lines.test.js b/hard/intersecting_lines.test.js
@@ -0,0 +1,45 @@
+const intersectingLines = require('./intersecting_lines');
+
+describe('intersectingLines()', () => {
+    test('passes Coderbyte.com tests', () => {
+        expect(intersectingLines(['(3,0)', '(1,4)', '(0,-3)', '(2,3)'])).toBe(
+            '(9/5,12/5)'
+        );
+
+        expect(
+            intersectingLines(['(0,15)', '(3,-12)', '(2,1)', '(13,7)'])
+        ).toBe('(166/105,27/35)');
+
+        expect(
+            intersectingLines(['(1,2)', '(3,4)', '(-5,-6)', '(-7,-8)'])
+        ).toBe('no intersection');
+
+        expect(
+            intersectingLines(['(10,11)', '(12,16)', '(6,7)', '(18,-4)'])
+        ).toBe('(318/41,221/41)');
+
+        expect(intersectingLines(['(0,0)', '(0,-1)', '(1,1)', '(0,1)'])).toBe(
+            '(0,1)'
+        );
+
+        expect(
+            intersectingLines(['(9,-2)', '(-2,9)', '(3,4)', '(10,11)'])
+        ).toBe('(3,4)');
+
+        expect(
+            intersectingLines(['(100,5)', '(6,2)', '(2,6)', '(5,100)'])
+        ).toBe('(170/91,170/91)');
+
+        expect(
+            intersectingLines(['(1,-1)', '(1,1)', '(-5,-5)', '(-7,-7)'])
+        ).toBe('(1,1)');
+
+        expect(
+            intersectingLines(['(6,12)', '(7,14)', '(-100,-3)', '(-3,-5)'])
+        ).toBe('(-491/196,-491/98)');
+
+        expect(
+            intersectingLines(['(4,3)', '(2,1)', '(-7,-6)', '(-4,-1)'])
+        ).toBe('(-10,-11)');
+    });
+});
