Add interpolation algo (#158)

* Add interpolation algo

* Update src/searching/interpolation-search.js

Co-authored-by: Minko Gechev <mgechev@gmail.com>

Author: duffman85

src/searching/interpolation-search.js

@@ -0,0 +1,54 @@
+(function(exports) {
+  'use strict';
+  /**
+   * Searches for specific element in a given array using
+   * the jump search algorithm.<br><br>
+   * Time complexity: O(log N).
+   *
+   * @example
+   *
+   * var search = require('path-to-algorithms/src/searching/'+
+   * 'interpolation-search').interpolationSearch;
+   * console.log(search([1, 2, 3, 4, 5], 4)); // 3
+   *
+   * @public
+   * @module searching/interpolation-search
+   * @param {Array} sortedArray Input array.
+   * @param {Number} seekIndex of the element which index should be found.
+   * @returns {Number} Index of the element or -1 if not found.
+   */
+  function interpolationSearch(sortedArray, seekIndex) {
+    let leftIndex = 0;
+    let rightIndex = sortedArray.length - 1;
+
+    while (leftIndex <= rightIndex) {
+      const rangeDiff = sortedArray[rightIndex] - sortedArray[leftIndex];
+      const indexDiff = rightIndex - leftIndex;
+      const valueDiff = seekIndex - sortedArray[leftIndex];
+
+      if (valueDiff < 0) {
+        return -1;
+      }
+
+      if (!rangeDiff) {
+        return sortedArray[leftIndex] === seekIndex ? leftIndex : -1;
+      }
+
+      const middleIndex =
+        leftIndex + Math.floor((valueDiff * indexDiff) / rangeDiff);
+
+      if (sortedArray[middleIndex] === seekIndex) {
+        return middleIndex;
+      }
+
+      if (sortedArray[middleIndex] < seekIndex) {
+        leftIndex = middleIndex + 1;
+      } else {
+        rightIndex = middleIndex - 1;
+      }
+    }
+
+    return -1;
+  }
+  exports.interpolationSearch = interpolationSearch;
+})(typeof window === 'undefined' ? module.exports : window);

test/searching/interpolation-search.spec.js

@@ -0,0 +1,22 @@
+var interpolationSearch = require('../../src/searching/interpolation-search')
+  .interpolationSearch;
+
+describe('Interpolation search', function() {
+  'use strict';
+
+  it('should find the element at position 0 ', function() {
+    expect(interpolationSearch([1, 2, 3, 4, 6, 8], 1)).toBe(0);
+  });
+
+  it('should find the element at position 4 ', function() {
+    expect(interpolationSearch([1, 2, 3, 4, 6, 8], 6)).toBe(4);
+  });
+
+  it('should return -1 if element is not found', function() {
+    expect(interpolationSearch([1, 2, 3, 4, 6, 8], 17)).toBe(-1);
+  });
+
+  it('should return -1 if array is empty', function() {
+    expect(interpolationSearch([], 10)).toBe(-1);
+  });
+});