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Commit bc95e85

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Kyle-SkiTheSTL
authored andcommitted
Add Ternary search (knaxus#76)
* implamenting ternary search * adding complexity * changed `ternarySearch` to be more like recursive, fixed recursive, tests now correct * fixing recursive search, removing unnecessary if
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const { ternarySearch, ternarySearchRecursive } = require('.');
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describe('Ternary Search', () => {
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const array = [1, 2, 3, 4, 5, 6, 7, 8];
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const low = 0;
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const high = array.length - 1;
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describe('When element to find is at 1st position ', () => {
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it('Ternary search with Loop', () => {
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expect(ternarySearch(array, 1)).toEqual(0);
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});
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it('Ternary serach with recursion', () => {
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expect(ternarySearchRecursive(array, low, high, 1)).toEqual(0);
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});
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});
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describe('When element to find is at last position ', () => {
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it('Ternary search with Loop', () => {
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expect(ternarySearch(array, 8)).toEqual(7);
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});
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it('Ternary serach with recursion', () => {
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expect(ternarySearchRecursive(array, low, high, 8)).toEqual(7);
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});
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});
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describe('When element to find is at random position ', () => {
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it('Ternary search with Loop', () => {
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expect(ternarySearch(array, 3)).toEqual(2);
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});
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it('Ternary serach with recursion', () => {
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expect(ternarySearchRecursive(array, low, high, 4)).toEqual(3);
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});
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});
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describe('When element to find is no present in array ', () => {
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it('Ternary search with Loop', () => {
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expect(ternarySearch(array, 10)).toEqual(null);
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});
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it('Ternary serach with recursion', () => {
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expect(ternarySearchRecursive(array, low, high, 10)).toEqual(null);
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});
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});
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});
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/**
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* Note: Array must be sorted for ternary search
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* Complexity:
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* Worst case time complexity: O(log N)
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* Average case time complexity: O(log N)
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* Best case time complexity: O(1)
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* Space complexity: O(1)
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*/
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function ternarySearch(arr, key){
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let low = 0;
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let high = arr.length - 1;
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while(low <= high){
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let lowMiddle = low + Math.floor((high - low) / 3);
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let highMiddle = low + 2 * Math.floor((high - low) / 3);
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if(key == arr[low]){
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return low;
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} else if(key == arr[high]){
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return high;
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} else if(key <= arr[lowMiddle]){
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high = lowMiddle;
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} else if(key > arr[lowMiddle] && key <= arr[highMiddle]){
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low = lowMiddle + 1;
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high = highMiddle;
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} else {
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low = highMiddle + 1;
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}
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}
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return null;
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}
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function ternarySearchRecursive(arr, low, high, key){
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if(high >= low){
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let highMiddle = low + 2 * Math.floor((high - low) / 3);
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let lowMiddle = low + Math.floor((high - low) / 3);
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if(key === arr[lowMiddle]){
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return lowMiddle;
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} else if(key === arr[highMiddle]){
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return highMiddle;
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} else if(key < arr[lowMiddle]){
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return ternarySearchRecursive(arr, low, lowMiddle - 1, key);
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} else if(key > arr[lowMiddle] && key < arr[highMiddle]){
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return ternarySearchRecursive(arr, lowMiddle + 1, highMiddle - 1, key);
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} else {
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return ternarySearchRecursive(arr, highMiddle + 1, high, key);
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}
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}
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return null;
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}
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module.exports = {
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ternarySearch,
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ternarySearchRecursive
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};

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