Added medium/histogram_area

bradhanson · bradhanson · commit c33b26ea092e · 2018-07-23T12:27:26.000-04:00
diff --git a/medium/histogram_area.js b/medium/histogram_area.js
@@ -0,0 +1,57 @@
+/**
+ * Using the JavaScript language, have the function histogramArea(arr) read the
+ * array of non-negative integers stored in arr which will represent the heights
+ * of bars on a graph (where each bar width is 1), and determine the largest
+ * area underneath the entire bar graph. For example: if arr is [2, 1, 3, 4, 1]
+ * then this looks like the following bar graph:
+ *
+ * [Image of Example Histogram](https://i.imgur.com/GyUx5Gh.jpg)
+ *
+ * You can see in the above bar graph that the largest area underneath the graph
+ * is covered by the x's. The area of that space is equal to 6 because the
+ * entire width is 2 and the maximum height is 3, therefore 2 * 3 = 6. Your
+ * program should return 6. The array will always contain at least 1 element.
+ *
+ * https://www.coderbyte.com/results/bhanson:Histogram%20Area:JavaScript
+ *
+ * @param  {array} arr
+ * @return {number}
+ */
+function histogramArea(arr) {
+    const histogram = arr;
+
+    // Generate combos
+    const combos = [];
+    for (let max = Math.pow(2, histogram.length), i = 0; i < max; i++) {
+        let combo = i.toString(2);
+        // Pad left
+        while (combo.length < histogram.length) {
+            combo = '0' + combo;
+        }
+
+        // 1s must be adjacent with no 0s in between
+        const goodComboRegEx = /^[0]*[1]+[0]*$/;
+        const goodCombo = goodComboRegEx.test(combo);
+        if (goodCombo) {
+            combos.push(combo);
+        }
+    }
+
+    let maxArea = 0;
+    combos.forEach(combo => {
+        const area = histogramAreaOfCombo(histogram, combo);
+        if (area > maxArea) {
+            maxArea = area;
+        }
+    });
+
+    return maxArea;
+}
+
+function histogramAreaOfCombo(histogram, combo) {
+    const hist = histogram.filter((element, index) => combo[index] === '1');
+    const maxHeight = Math.min(...hist);
+    return maxHeight * hist.length;
+}
+
+module.exports = histogramArea;
diff --git a/medium/histogram_area.test.js b/medium/histogram_area.test.js
@@ -0,0 +1,11 @@
+const histogramArea = require('./histogram_area');
+
+describe('histogramArea()', () => {
+    test('finds max rectangle area of histogram', () => {
+        expect(histogramArea([2, 1, 3, 4, 1])).toBe(6);
+
+        expect(histogramArea([6, 3, 1, 4, 12, 4])).toBe(12);
+
+        expect(histogramArea([5, 6, 7, 4, 1])).toBe(16);
+    });
+});
