Added medium/three_points

bradhanson · bradhanson · commit 634e6f9928d2 · 2018-08-06T20:14:14.000-04:00
diff --git a/medium/three_points.js b/medium/three_points.js
@@ -0,0 +1,44 @@
+/**
+ * Using the JavaScript language, have the function threePoints(strArr) read the
+ * array of strings stored in strArr which will always contain 3 elements and be
+ * in the form: ["(x1,y1)", "(x2,y2)", "(x3,y3)"]. Your goal is to first create
+ * a line formed by the first two points (that starts from the first point and
+ * moves in the direction of the second point and that stretches in both
+ * directions through the two points), and then determine what side of the line
+ * point 3 is on. The result will either be right, left, or neither. For
+ * example: if strArr is ["(1,1)", "(3,3)", "(2,0)"] then your program should
+ * return the string right because the third point lies to the right of the line
+ * formed by the first two points.
+ *
+ * https://www.coderbyte.com/results/bhanson:Three%20Points:JavaScript
+ *
+ * @param  {array} strArr
+ * @return {string} 'right', 'left', or 'neither'
+ */
+function threePoints(strArr) {
+    // Parse input
+    const [pointA, pointB, pointX] = strArr.map(point => {
+        const [, x, y] = point.match(/\((-?[\d]+),(-?[\d]+)\)/).map(Number);
+        return { x, y };
+    });
+
+    // y = mx + b
+    const slope = (pointB.y - pointA.y) / (pointB.x - pointA.x); // m
+    const yIntercept = (pointA.y - slope) / pointA.x; // b
+
+    // x = (y - b) / m
+    let x;
+    if (slope === Infinity) {
+        x = pointX.x;
+    } else {
+        x = pointX.y - yIntercept + slope;
+    }
+
+    if (x === 0 || Number.isNaN(x)) {
+        return 'neither';
+    }
+
+    return x < 0 ? 'left' : 'right';
+}
+
+module.exports = threePoints;
diff --git a/medium/three_points.test.js b/medium/three_points.test.js
@@ -0,0 +1,36 @@
+const threePoints = require('./three_points');
+
+describe('threePoints()', () => {
+    test('correctly returns side of point relative to line', () => {
+        expect(threePoints(['(1,1)', '(3,3)', '(2,0)'])).toBe('right');
+
+        expect(threePoints(['(0,-3)', '(-2,0)', '(0,0)'])).toBe('right');
+
+        expect(threePoints(['(0,0)', '(0,5)', '(0,2)'])).toBe('neither');
+    });
+
+    test('passes Coderbyte.com tests', () => {
+        expect(threePoints(['(1,1)', '(3,3)', '(2,0)'])).toBe('right');
+
+        expect(threePoints(['(0,-3)', '(-2,0)', '(0,0)'])).toBe('right');
+
+        expect(threePoints(['(0,0)', '(0,5)', '(0,2)'])).toBe('neither');
+
+        expect(threePoints(['(0,0)', '(0,5)', '(-2,2)'])).toBe('left');
+
+        expect(threePoints(['(0,0)', '(0,100)', '(-200,5)'])).toBe('left');
+
+        expect(threePoints(['(-3,0)', '(0,1)', '(-1,0)'])).toBe('right');
+
+        expect(threePoints(['(0,1)', '(-3,0)', '(-1,0)'])).toBe('left');
+
+        expect(threePoints(['(0,5)', '(0,-5)', '(1,1)'])).toBe('left');
+
+        // TODO: Fix to pass this test
+        expect(threePoints(['(100,100)', '(-1,-1)', '(5,1)'])).toBe('left');
+
+        expect(threePoints(['(5000,5001)', '(-5001,-5000)', '(0,601)'])).toBe(
+            'right'
+        );
+    });
+});
