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Commit bd588c2

Browse files
allow ++ on for loops
1 parent bc491d5 commit bd588c2

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4 files changed

+54
-34
lines changed

4 files changed

+54
-34
lines changed

‎.eslintrc.js‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,7 @@ module.exports = {
1212

1313
// https://eslint.org/docs/rules/no-plusplus
1414
// allows unary operators ++ and -- in the afterthought (final expression) of a for loop.
15-
"allowForLoopAfterthoughts": true,
15+
"no-plusplus": [2,{"allowForLoopAfterthoughts": true}],
1616

1717
// Allow for..of
1818
"no-restricted-syntax": [0, "ForOfStatement"],
Lines changed: 13 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,8 @@
11
/**
2-
* 8.7 Permutations without Dups: Write a method to compute all permutations of a string of unique characters.
2+
* 8.7 Permutations without Dups:
3+
*
4+
* Write a method to compute all permutations of
5+
* a string of unique characters.
36
*
47
* @param string
58
* @param prefix
@@ -9,19 +12,18 @@
912
function permutations(string = '', prefix = '', memo = {}) {
1013
if (string.length < 2) {
1114
return [prefix + string];
12-
} else if (string.length == 2) {
15+
} else if (string.length === 2) {
1316
return [prefix + string, prefix + string[1] + string[0]];
1417
} else if (memo[string]) {
15-
return memo[string].map((e) => prefix + e);
16-
} else {
17-
let results = [];
18-
for (var i = 0; i < string.length; i++) {
19-
const letter = string[i];
20-
results = results.concat(permutations(string.replace(letter, ''), letter, memo));
21-
}
22-
memo[string] = results;
23-
return results.map((e) => prefix + e);
18+
return memo[string].map(e => prefix + e);
19+
}
20+
let results = [];
21+
for (let i = 0; i < string.length; i++) {
22+
const letter = string[i];
23+
results = results.concat(permutations(string.replace(letter, ''), letter, memo));
2424
}
25+
memo[string] = results;
26+
return results.map(e => prefix + e);
2527
}
2628

2729
module.exports = permutations;

‎src/algorithms/combination-sum.js‎

Lines changed: 32 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -8,33 +8,44 @@ function combinationSum(
88
target,
99
solution = [],
1010
current = [],
11-
currentSum = 0,
1211
index = 0,
1312
) {
14-
if (currentSum === target) {
15-
solution.push(current);
13+
if (target < 0) {
14+
// By adding another candidate we've gone below zero.
15+
// This would mean that the last candidate was not acceptable.
16+
return solution;
1617
}
1718

18-
let candidate = candidates[index];
19-
let newSum = currentSum + candidate;
20-
let newCurrent = current.concat(candidate);
21-
22-
if (newSum <= target) {
23-
combinationSum(candidates, target, solution, newCurrent, newSum, index);
24-
} else if (index < candidates.length - 1) {
25-
const newIndex = index + 1;
26-
candidate = candidates[newIndex];
27-
newSum = currentSum;
28-
const reducedCurrent = current.slice(); // clone current
29-
while (newSum + candidate > target) {
30-
const deletedCandidate = reducedCurrent.pop();
31-
newSum -= deletedCandidate;
32-
}
33-
newSum += candidate;
34-
newCurrent = reducedCurrent.concat(candidate);
35-
combinationSum(candidates, target, solution, newCurrent, newSum, newIndex);
19+
if (target === 0) {
20+
// If after adding the previous candidate our remaining sum
21+
// became zero - we need to save the current combination since it is one
22+
// of the answers we're looking for.
23+
solution.push(current.slice());
24+
25+
return solution;
3626
}
3727

28+
// If we haven't reached zero yet let's continue to add all
29+
// possible candidates that are left.
30+
for (let candidateIndex = index; candidateIndex < candidates.length; candidateIndex += 1) {
31+
const currentCandidate = candidates[candidateIndex];
32+
33+
// Let's try to add another candidate.
34+
current.push(currentCandidate);
35+
36+
// Explore further option with current candidate being added.
37+
combinationSum(
38+
candidates,
39+
target - currentCandidate,
40+
solution,
41+
current,
42+
candidateIndex,
43+
);
44+
45+
// BACKTRACKING.
46+
// Let's get back, exclude current candidate and try another ones later.
47+
current.pop();
48+
}
3849

3950
return solution;
4051
}

‎src/algorithms/combination-sum.spec.js‎

Lines changed: 8 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -17,10 +17,17 @@ describe('combinationSum', () => {
1717
expect(combinationSum([2], 1)).toEqual([]);
1818
});
1919

20-
fit('should not find solution', () => {
20+
it('should find solution using two values', () => {
2121
expect(combinationSum([1, 2], 3)).toEqual([
2222
[1, 1, 1],
2323
[1, 2],
2424
]);
2525
});
26+
27+
it('should move on with next index', () => {
28+
expect(combinationSum([1, 10, 2], 3)).toEqual([
29+
[1, 1, 1],
30+
[1, 2],
31+
]);
32+
});
2633
});

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