pax_global_header00006660000000000000000000000064126610654770014530gustar00rootroot0000000000000052 comment=f6ca6ce8bb412772ade017d2c78d38d74ef8070e quickselect-1.0.0/000077500000000000000000000000001266106547700140425ustar00rootroot00000000000000quickselect-1.0.0/README.md000066400000000000000000000016371266106547700153300ustar00rootroot00000000000000## quickselect A tiny and fast [selection algorithm](https://en.wikipedia.org/wiki/Selection_algorithm) in JavaScript (specifically, [Floyd-Rivest selection](https://en.wikipedia.org/wiki/Floyd%E2%80%93Rivest_algorithm)). ```js quickselect(array, k[, left, right, compareFn]); ``` Rearranges items so that all items in the `[left, k]` are the smallest. The `k`-th element will have the `(k - left + 1)`-th smallest value in `[left, right]`. - `array`: the array to partially sort (in place) - `k`: middle index for partial sorting (as defined above) - `left`: left index of the range to sort (`0` by default) - `right`: right index (last index of the array by default) - `compareFn`: compare function Example: ```js var arr = [65, 28, 59, 33, 21, 56, 22, 95, 50, 12, 90, 53, 28, 77, 39]; quickselect(arr, 8); // [39, 28, 28, 33, 21, 12, 22, 50, 53, 56, 59, 65, 90, 77, 95] // ^^ 8th item ``` quickselect-1.0.0/index.js000066400000000000000000000032301266106547700155050ustar00rootroot00000000000000'use strict'; module.exports = partialSort; // Floyd-Rivest selection algorithm: // Rearrange items so that all items in the [left, k] range are smaller than all items in (k, right]; // The k-th element will have the (k - left + 1)th smallest value in [left, right] function partialSort(arr, k, left, right, compare) { left = left || 0; right = right || (arr.length - 1); compare = compare || defaultCompare; while (right > left) { if (right - left > 600) { var n = right - left + 1; var m = k - left + 1; var z = Math.log(n); var s = 0.5 * Math.exp(2 * z / 3); var sd = 0.5 * Math.sqrt(z * s * (n - s) / n) * (m - n / 2 < 0 ? -1 : 1); var newLeft = Math.max(left, Math.floor(k - m * s / n + sd)); var newRight = Math.min(right, Math.floor(k + (n - m) * s / n + sd)); partialSort(arr, k, newLeft, newRight, compare); } var t = arr[k]; var i = left; var j = right; swap(arr, left, k); if (compare(arr[right], t) > 0) swap(arr, left, right); while (i < j) { swap(arr, i, j); i++; j--; while (compare(arr[i], t) < 0) i++; while (compare(arr[j], t) > 0) j--; } if (compare(arr[left], t) === 0) swap(arr, left, j); else { j++; swap(arr, j, right); } if (j <= k) left = j + 1; if (k <= j) right = j - 1; } } function swap(arr, i, j) { var tmp = arr[i]; arr[i] = arr[j]; arr[j] = tmp; } function defaultCompare(a, b) { return a < b ? -1 : a > b ? 1 : 0; } quickselect-1.0.0/package.json000066400000000000000000000010031266106547700163220ustar00rootroot00000000000000{ "name": "quickselect", "version": "1.0.0", "description": "A tiny and fast selection algorithm in JavaScript.", "main": "index.js", "dependencies": {}, "devDependencies": { "eslint": "^2.1.0", "eslint-config-mourner": "^2.0.0", "tape": "^4.4.0" }, "scripts": { "pretest": "eslint index.js test.js", "test": "tape test.js" }, "keywords": ["selection", "algorithm", "quickselect", "sort", "partial", "floyd", "rivest"], "author": "Vladimir Agafonkin", "license": "ISC" } quickselect-1.0.0/test.js000066400000000000000000000004751266106547700153650ustar00rootroot00000000000000'use strict'; var test = require('tape').test; var quickselect = require('./'); test('selection', function (t) { var arr = [65, 28, 59, 33, 21, 56, 22, 95, 50, 12, 90, 53, 28, 77, 39]; quickselect(arr, 8); t.deepEqual(arr, [39, 28, 28, 33, 21, 12, 22, 50, 53, 56, 59, 65, 90, 77, 95]); t.end(); });