Add Pascal's triangle.

src/algorithms/math/pascal-triangle/README.md

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+# Pascal's Triangle
+
+In mathematics, **Pascal's triangle** is a triangular array of 
+the binomial coefficients.
+
+The rows of Pascal's triangle are conventionally enumerated 
+starting with row `n = 0` at the top (the `0th` row). The 
+entries in each row are numbered from the left beginning 
+with `k = 0` and are usually staggered relative to the 
+numbers in the adjacent rows. The triangle may be constructed
+in the following manner: In row `0` (the topmost row), there 
+is a unique nonzero entry `1`. Each entry of each subsequent
+row is constructed by adding the number above and to the 
+left with the number above and to the right, treating blank 
+entries as `0`. For example, the initial number in the 
+first (or any other) row is `1` (the sum of `0` and `1`),
+whereas the numbers `1` and `3` in the third row are added 
+to produce the number `4` in the fourth row.
+
+![Pascal's Triangle](https://upload.wikimedia.org/wikipedia/commons/0/0d/PascalTriangleAnimated2.gif)
+
+## Formula
+
+The entry in the `nth` row and `kth` column of Pascal's 
+triangle is denoted ![Formula](https://wikimedia.org/api/rest_v1/media/math/render/svg/206415d3742167e319b2e52c2ca7563b799abad7).
+For example, the unique nonzero entry in the topmost 
+row is ![Formula example](https://wikimedia.org/api/rest_v1/media/math/render/svg/b7e35f86368d5978b46c07fd6dddca86bd6e635c).
+
+With this notation, the construction of the previous 
+paragraph may be written as follows:
+
+![Formula](https://wikimedia.org/api/rest_v1/media/math/render/svg/203b128a098e18cbb8cf36d004bd7282b28461bf)
+
+for any non-negative integer `n` and any 
+integer `k` between `0` and `n`, inclusive.
+
+## References
+
+- [Wikipedia](https://en.wikipedia.org/wiki/Pascal%27s_triangle)

src/algorithms/math/pascal-triangle/__test__/pascalTriangleRecursive.test.js

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+import pascalTriangleRecursive from '../pascalTriangleRecursive';
+
+describe('pascalTriangleRecursive', () => {
+  it('should calculate Pascal Triangle coefficients for specific line number', () => {
+    expect(pascalTriangleRecursive(0)).toEqual([1]);
+    expect(pascalTriangleRecursive(1)).toEqual([1, 1]);
+    expect(pascalTriangleRecursive(2)).toEqual([1, 2, 1]);
+    expect(pascalTriangleRecursive(3)).toEqual([1, 3, 3, 1]);
+    expect(pascalTriangleRecursive(4)).toEqual([1, 4, 6, 4, 1]);
+    expect(pascalTriangleRecursive(5)).toEqual([1, 5, 10, 10, 5, 1]);
+    expect(pascalTriangleRecursive(6)).toEqual([1, 6, 15, 20, 15, 6, 1]);
+    expect(pascalTriangleRecursive(7)).toEqual([1, 7, 21, 35, 35, 21, 7, 1]);
+  });
+});

src/algorithms/math/pascal-triangle/pascalTriangleRecursive.js

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+/**
+ * @param {number} lineNumber
+ * @return {number[]}
+ */
+export default function pascalTriangleRecursive(lineNumber) {
+  if (lineNumber === 0) {
+    return [1];
+  }
+
+  const currentLineSize = lineNumber + 1;
+  const previousLineSize = currentLineSize - 1;
+
+  // Create container for current line values.
+  const currentLine = [];
+
+  // We'll calculate current line based on previous one.
+  const previousLine = pascalTriangleRecursive(lineNumber - 1);
+
+  // Let's go through all elements of current line except the first and
+  // last one (since they were and will be filled with 1's) and calculate
+  // current coefficient based on previous line.
+  for (let numIndex = 0; numIndex < currentLineSize; numIndex += 1) {
+    const leftCoefficient = (numIndex - 1) >= 0 ? previousLine[numIndex - 1] : 0;
+    const rightCoefficient = numIndex < previousLineSize ? previousLine[numIndex] : 0;
+
+    currentLine[numIndex] = leftCoefficient + rightCoefficient;
+  }
+
+  return currentLine;
+}