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const defaultKey = (arr) => arr.join(""); | |
function createPermute(toKey = defaultKey) { | |
return function* permute(arr, length = arr.length) { | |
if (length > arr.length) { | |
throw new Error( | |
`The permutation size required (${length}) is greater than the size of the array supplied (${arr.length}).` | |
); | |
} | |
if (arr.length === 0) { | |
return; | |
} | |
if (arr.length === 1) { | |
yield [arr[0]]; | |
return; | |
} | |
if (arr.length === 2) { | |
const [a, b] = arr; | |
yield [a, b]; | |
yield [b, a]; | |
return; | |
} | |
let seen = new Set(); | |
for (let idx = 0; idx < arr.length; idx++) { | |
const first = arr[idx]; | |
const tail = [...arr]; | |
tail.splice(idx, 1); | |
for (let part of permute(tail, length - 1)) { | |
const permutation = [first, ...part].slice(0, length); | |
const key = toKey(permutation); | |
if (seen.has(key)) { | |
continue; | |
} | |
seen.add(key); | |
yield permutation; | |
} | |
} | |
}; | |
} | |
function kSum(k) { | |
const combinations = createPermute((arr) => | |
[...arr].sort((a, b) => a - b).join("") | |
); | |
const sum = (values) => values.reduce((a, b) => a + b, 0); | |
return function* (arr, target = 0) { | |
for (let values of combinations(arr, k)) { | |
if (sum(values) === target) { | |
yield values; | |
} | |
} | |
}; | |
} | |
const threeSum = kSum(3); | |
const fourSum = kSum(4); | |
console.log("threeSum", Array.from(threeSum([-1, 0, 1]))); | |
console.log("fourSum", Array.from(fourSum([-1, -1, 1, 1, 0, 0, -2, 2, -4, 6]))); |
function* threeSum(_nums, target = 0) {
const nums = [..._nums].sort((a, b) => a - b);
for (let adx = 0; adx < nums.length - 2; adx++) {
const a = nums[adx];
let bdx = adx + 1;
let cdx = nums.length - 1;
while (bdx < cdx) {
const b = nums[bdx];
const c = nums[cdx];
const sum = a + b + c;
if (sum === target) {
yield [a, b, c];
while (bdx < cdx && b === nums[bdx + 1]) bdx++;
while (bdx < cdx && c === nums[cdx - 1]) cdx--;
bdx++;
cdx--;
} else if (sum < target) {
bdx++;
} /* if (sum > target) */ else {
cdx--;
}
}
while (a === nums[adx + 1]) adx++;
}
}
for (let values of threeSum([-1, 0, 1, 2, -1, -4, -2, -3, 3, 0, 4])) {
console.log("threeSum", values);
}
See: https://codesandbox.io/s/patient-dream-2hiwx?file=/src/index.js:0-799
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This first version was based on my original permutations/combinations code.
See: https://codesandbox.io/s/elastic-montalcini-q6s5j?file=/src/index.js:0-1326
I realise this is likely very inefficient and that the recursion is dangerous due to stack overflows however it's a working solution. I'll go back to the drawing board for the next version...!