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const powerset = arr =>arr.reduce((a, v) => a.concat(a.map(r => r.concat(v))), [[]]);powerset([1, 2]); // [[], [1], [2], [1, 2]]
const kMeans = (data, k = 1) => {const centroids = data.slice(0, k);const distances = Array.from({ length: data.length }, () =>Array.from({ length: k }, () => 0));const classes = Array.from({ length: data.length }, () => -1);let itr = true;while (itr) {itr = false;for (let d in data) {for (let c = 0; c < k; c++) {distances[d][c] = Math.hypot(...Object.keys(data[0]).map(key => data[d][key] - centroids[c][key]));}const m = distances[d].indexOf(Math.min(...distances[d]));if (classes[d] !== m) itr = true;classes[d] = m;}for (let c = 0; c < k; c++) {centroids[c] = Array.from({ length: data[0].length }, () => 0);const size = data.reduce((acc, _, d) => {if (classes[d] === c) {acc++;for (let i in data[0]) centroids[c][i] += data[d][i];}return acc;}, 0);for (let i in data[0]) {centroids[c][i] = parseFloat(Number(centroids[c][i] / size).toFixed(2));}}}return classes;};kMeans([[0, 0], [0, 1], [1, 3], [2, 0]], 2); // [0, 1, 1, 0]
const head = arr => (arr && arr.length ? arr[0] : undefined);head([1, 2, 3]); // 1head([]); // undefinedhead(null); // undefinedhead(undefined); // undefined
const getSubsets = arr => arr.reduce((prev, curr) => prev.concat(prev.map(k => k.concat(curr))), [[]]);// ExamplesgetSubsets([1, 2]); // [[], [1], [2], [1, 2]]getSubsets([1, 2, 3]); // [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]
/*** @param {number[]} nums* @param {number} target* @return {number[]}*/var twoSum = function(nums, target) {for(let i = 0; i < nums.length; i++) {for(let j = 0; j < nums.length; j++) {if(nums[i] + nums[j] === target && i !== j) {return [i, j]}}}};
function Clock(props) {return (<div><h1>Hello, world!</h1><h2>It is {props.date.toLocaleTimeString()}.</h2></div>);}function tick() {ReactDOM.render(<Clock date={new Date()} />,document.getElementById('root'));}setInterval(tick, 1000);