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subset/powerset problem

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Lines changed: 18 additions & 0 deletions

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	`1`	`+/**`
	`2`	`+ *`
	`3`	`+ * @param {*} nums`
	`4`	`+ */`
	`5`	`+function subsetBacktrack(nums, start = 0, current = [], result = []) {`
	`6`	`+ // console.log({ nums, start, current, result });`
	`7`	`+ result.push([...current]);`
	`8`	`+`
	`9`	`+ for (let i = start; i < nums.length; i++) {`
	`10`	`+ current.push(nums[i]);`
	`11`	`+ subsetBacktrack(nums, i + 1, current, result);`
	`12`	`+ current.pop();`
	`13`	`+ // console.log(current.pop());`
	`14`	`+ }`
	`15`	`+ return result;`
	`16`	`+}`
	`17`	`+`
	`18`	`+module.exports = subsetBacktrack;`

Lines changed: 27 additions & 0 deletions

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	`1`	`+/**`
	`2`	`+ * Bitmask approach`
	`3`	`+ * @param {number[]} nums`
	`4`	`+ * @return {number[][]}`
	`5`	`+ */`
	`6`	`+function subsetsBinary(nums) {`
	`7`	`+ const len = nums.length;`
	`8`	`+ const max = 2 ** len;`
	`9`	`+ const result = [];`
	`10`	`+`
	`11`	`+ for (let bin = 0; bin < max; bin++) {`
	`12`	`+ const bitmask = bin.toString(2).padStart(len, '0');`
	`13`	`+`
	`14`	`+ const el = Array.from(bitmask).reduce((a, bit, i) => {`
	`15`	`+ if (bit === '1') {`
	`16`	`+ return a.concat(nums[i]);`
	`17`	`+ }`
	`18`	`+ return a;`
	`19`	`+ }, []);`
	`20`	`+`
	`21`	`+ result.push(el);`
	`22`	`+ }`
	`23`	`+`
	`24`	`+ return result;`
	`25`	`+}`
	`26`	`+`
	`27`	`+module.exports = subsetsBinary;`

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	`1`	`+/**`
	`2`	`+ *`
	`3`	`+ * https://leetcode.com/problems/subsets`
	`4`	`+ * @param {number[]} nums`
	`5`	`+ * @return {number[][]}`
	`6`	`+ */`
	`7`	`+function subsetsConcat(nums) {`
	`8`	`+ return nums.reduce((result, n) => {`
	`9`	`+ const newSet = result.map(r => r.concat(n));`
	`10`	`+ return result.concat(newSet); // O(n * n^2) bcuz copy`
	`11`	`+ }, [`
	`12`	`+ [],`
	`13`	`+ ]);`
	`14`	`+}`
	`15`	`+`
	`16`	`+module.exports = subsetsConcat;`

Lines changed: 46 additions & 0 deletions

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	`1`	`+// npx jest lab/exercises/01-arrays/powerset/powerset.spec.js --watch`
	`2`	`+`
	`3`	`+const backtrack = require('./powerset-backtrack');`
	`4`	`+const subsetsBinary = require('./powerset-binaryNumbers');`
	`5`	`+const subsetsConcat = require('./powerset-concat');`
	`6`	`+`
	`7`	`+const approaches = [backtrack, subsetsBinary, subsetsConcat];`
	`8`	`+`
	`9`	`+approaches.forEach((approach) => {`
	`10`	+ describe(`Powerset ${approach.name}`, () => {
	`11`	`+ it('should work with 0 elements', () => {`
	`12`	`+ expect(approach([])).toEqual([`
	`13`	`+ [],`
	`14`	`+ ]);`
	`15`	`+ });`
	`16`	`+`
	`17`	`+ it('should work with 1 element', () => {`
	`18`	`+ expect(approach([1])).toEqual([`
	`19`	`+ [],`
	`20`	`+ [1],`
	`21`	`+ ]);`
	`22`	`+ });`
	`23`	`+`
	`24`	`+ it('should work with 2 elements', () => {`
	`25`	`+ expect(approach([1, 2])).toEqual(expect.arrayContaining([`
	`26`	`+ [],`
	`27`	`+ [1],`
	`28`	`+ [2],`
	`29`	`+ [1, 2],`
	`30`	`+ ]));`
	`31`	`+ });`
	`32`	`+`
	`33`	`+ it('should work with 3 elements', () => {`
	`34`	`+ expect(approach([1, 2, 3])).toEqual(expect.arrayContaining([`
	`35`	`+ [],`
	`36`	`+ [1],`
	`37`	`+ [2],`
	`38`	`+ [1, 2],`
	`39`	`+ [3],`
	`40`	`+ [2, 3],`
	`41`	`+ [1, 3],`
	`42`	`+ [1, 2, 3],`
	`43`	`+ ]));`
	`44`	`+ });`
	`45`	`+ });`
	`46`	`+});`

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