Add day 20

Author: MadhavBahl

README.md

@@ -36,6 +36,7 @@ Read [CONTRIBUTING.md](./CONTRIBUTING.md) for contribution guidelines.
 17. [Day 17 -- N Queens Problem](./day17) -- [http://codetoexpress.tech/dc/day17/](http://codetoexpress.tech/dc/day17/)
 18. [Day 18 -- Frequency Count and Check Power N](./day18) -- [http://codetoexpress.tech/dc/day18/](http://codetoexpress.tech/dc/day18/)
 19. [Day 19 -- Cartesian Product and Shuffle Algorithm](./day19) -- [http://codetoexpress.tech/dc/day19/](http://codetoexpress.tech/dc/day19/)
+20. [Day 20 -- Array Partition](./day20) -- [http://codetoexpress.tech/dc/day20/](http://codetoexpress.tech/dc/day20/)
 
 ## [More Problems](./BONUS/README.md)
 

day20/JavaScript/sol1.js

@@ -0,0 +1,37 @@
+/**
+ * @author MadhavBahlMD
+ * @date 16/01/2019
+ */
+
+/* ========================================= */
+/* ===== Array Partition Problem In JS ===== */
+/* ========================================= */
+
+function partition (array, size) {
+    let partitionedArray = [],
+        toBeAdded = [];
+
+    for (let i=0; i<array.length; i++) {
+        if ((i)%size === 0) {
+            if (toBeAdded.length > 0)  partitionedArray.push (toBeAdded);
+            toBeAdded = [];
+        }
+        toBeAdded.push (array[i]);
+    }
+    if (toBeAdded.length > 0)  partitionedArray.push (toBeAdded);
+    return partitionedArray;
+}
+
+// Test our partition function
+console.log(partition ([1,2,3,4,5,6,7,8], 2));
+console.log(partition ([1,2,3,4,5,6,7], 2));
+console.log(partition ([1,2,5,3,4,6,7,1,2,4,6,4,5], 3));
+console.log(partition ([1,2,5,3,4,6,7,1,2,4,6,4,5], 4));
+
+/**
+ * Required Output
+ * [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ] ]
+ * [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7 ] ]
+ * [ [ 1, 2, 5 ], [ 3, 4, 6 ], [ 7, 1, 2 ], [ 4, 6, 4 ], [ 5 ] ]
+ * [ [ 1, 2, 5, 3 ], [ 4, 6, 7, 1 ], [ 2, 4, 6, 4 ], [ 5 ] ]
+ */

day20/JavaScript/sol2.js

@@ -0,0 +1,38 @@
+/**
+ * @author MadhavBahlMD
+ * @date 16/01/2019
+ */
+
+/* ========================================= */
+/* ===== Array Partition Problem In JS ===== */
+/* ========================================= */
+
+function partition (array, size) {
+    let partitionedArray = [];
+
+    for (let element of array) {
+        let partition = partitionedArray[partitionedArray.length - 1];
+        
+        if (!partition || partition.length === size) {
+            partitionedArray.push ([element]);
+        } else {
+            lastEle.push (element);
+        }
+    }
+
+    return partitionedArray;
+}
+
+// Test our partition function
+console.log(partition ([1,2,3,4,5,6,7,8], 2));
+console.log(partition ([1,2,3,4,5,6,7], 2));
+console.log(partition ([1,2,5,3,4,6,7,1,2,4,6,4,5], 3));
+console.log(partition ([1,2,5,3,4,6,7,1,2,4,6,4,5], 4));
+
+/**
+ * Required Output
+ * [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ] ]
+ * [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7 ] ]
+ * [ [ 1, 2, 5 ], [ 3, 4, 6 ], [ 7, 1, 2 ], [ 4, 6, 4 ], [ 5 ] ]
+ * [ [ 1, 2, 5, 3 ], [ 4, 6, 7, 1 ], [ 2, 4, 6, 4 ], [ 5 ] ]
+ */

day20/JavaScript/sol3.js

@@ -0,0 +1,33 @@
+/**
+ * @author MadhavBahlMD
+ * @date 16/01/2019
+ */
+
+/* ========================================= */
+/* ===== Array Partition Problem In JS ===== */
+/* ========================================= */
+
+function partition (array, size) {
+    let partitionedArray = [], i=0;
+
+    while (i<array.length) {
+        partitionedArray.push (array.slice(i, i+size));
+        i += size;
+    }
+
+    return partitionedArray;
+}
+
+// Test our partition function
+console.log(partition ([1,2,3,4,5,6,7,8], 2));
+console.log(partition ([1,2,3,4,5,6,7], 2));
+console.log(partition ([1,2,5,3,4,6,7,1,2,4,6,4,5], 3));
+console.log(partition ([1,2,5,3,4,6,7,1,2,4,6,4,5], 4));
+
+/**
+ * Required Output
+ * [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7, 8 ] ]
+ * [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7 ] ]
+ * [ [ 1, 2, 5 ], [ 3, 4, 6 ], [ 7, 1, 2 ], [ 4, 6, 4 ], [ 5 ] ]
+ * [ [ 1, 2, 5, 3 ], [ 4, 6, 7, 1 ], [ 2, 4, 6, 4 ], [ 5 ] ]
+ */

day20/README.md

@@ -0,0 +1,81 @@
+![cover](./cover.png)
+
+# Day 20 - Array Partition
+
+Write a program to divide the given array into sub arrays where each sub array is of the length equal to the given partition size.
+
+## Example
+
+partition([1,2,3,4,5,6,7,8], 2) --> [[1, 2], [3, 4], [5, 6], [7, 8]]
+partition([1,2,3,4,5,6,7], 2) --> [[1, 2], [3, 4], [5, 6], [7]]
+
+## JavaScript Solution(s)
+
+### [Solution 1](./JavaScript/sol1.js)
+
+A very simple solution, all we have to is loop through i=0 to array length. In each iteration we check whether current iteration (i) is divisible by size or not, if it is not divisible, we add the current element in `toBeAdded` array otherwise we push the `toBeAdded` array into `partitionedArray`. Also, we check that `toBeAdded` is not wmpty otherwise it will push an empty array to `partitionedArray`
+
+
+```js
+function partition (array, size) {
+    let partitionedArray = [],
+        toBeAdded = [];
+
+    for (let i=0; i<array.length; i++) {
+        if ((i)%size === 0) {
+            if (toBeAdded.length > 0)  partitionedArray.push (toBeAdded);
+            toBeAdded = [];
+        }
+        toBeAdded.push (array[i]);
+    }
+    if (toBeAdded.length > 0)  partitionedArray.push (toBeAdded);
+    return partitionedArray;
+}
+```
+
+### [Solution 2](./JavaScript/sol2.js)
+
+The second solution is also similar to the first one. Here, we create an empty array to hold partitions (let's call the array `partitionedArray`). Now for each element in the "original" array, we retrieve the  last element in partitionedArray . If the last element does not exist (in case of empty array), or if it's size is equal to the partition size, we push a new partition array into the `partitionedArray` with the current element. Otherwise, we add the current element into the partition.
+
+```js
+function partition (array, size) {
+    let partitionedArray = [];
+
+    for (let element of array) {
+        let partition = partitionedArray[partitionedArray.length - 1];
+        if (!partition || partition.length === size) {
+            partitionedArray.push ([element]);
+        } else {
+            lastEle.push (element);
+        }
+    }
+
+    return partitionedArray;
+}
+```
+
+### [Solution 3](./JavaScript/sol3.js)
+
+This method will use JavaScript's `slice` method. This is probably the easiest method due to the inbuilt function `slice`. 
+
+#### How slice works
+
+array.sllice (startIndex, endIndex); will return a subarray of array including elements from startIndex to endIndex (**not including endIndex**).
+
+#### Steps
+
+- Create an empty `partitionedArray` array
+- run a while loop from index i=0 to less than "original" array.length
+- Push a `slice` of length `size` from `array` to `partitionedArray`.
+- `index = index+size`
+
+```js
+function partition (array, size) {
+    let partitionedArray = [], i=0;
+    while (i<array.length) {
+        partitionedArray.push (array.slice(i, i+size));
+        i += size;
+    }
+    return partitionedArray;
+}
+```