【前端面试】七、算法-数组展平

目录

1.判断数组

 2.二维数组展平

3.多维数组展平

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1.判断数组

    // 判断数组console.log([].constructor === Array);console.log( Array.isArray([]));console.log( [] instanceof Array);console.log(Object.prototype.toString.call([]) === '[object Array]');

 2.二维数组展平

    const flattenOnce = (arr) => {return [].concat(...arr)}const arr1 = [1, [2, 3], [4, 5, 6], [7, 8, 9, 10]];console.log('flattenOnce',flattenOnce(arr1));

3.多维数组展平

递归

    // 多维数组展平const arr2 = [1, [2, 3], [4, 5, 6], [7, 8, 9, 10], [11, [12, 13, [14, 15]]]];// 递归const flatten1 = (arr) => {return arr.reduce((acc, cur) => {return acc.concat(Array.isArray(cur) ? flatten1(cur) : cur)}, [])}console.log('flatten1',flatten1(arr2));// 递归const flatten2 = (arr) => {return [].concat(...arr.map(item => Array.isArray(item) ? flatten2(item) : item))}console.log('flatten2',flatten2(arr2));

字符串

    function flatten3(arr) {return arr.toString().split(',').map(item => +item)}console.log('flatten3',flatten3(arr2));

循环

    const flatten4 = (arr) => {while(arr.some(item => Array.isArray(item))) {arr = [].concat(...arr)}return arr}console.log('flatten4',flatten4(arr2));

栈的思想

    const flatten5 = arr => {let stack = arr.slice()const r = []while (stack.length) {const item = stack.pop()if(Array.isArray(item)){stack = stack.concat(item) //stack.push(...item)} else {r.unshift(item)}}return r}console.log('flatten5',flatten5(arr2));

生成器 

    function *flatten6(arr){for (let i = 0; i < arr.length; i++) {if(Array.isArray(arr[i])) {yield *flatten3(arr[i])} else{yield arr[i]}}}console.log('flatten6', [...flatten6(arr2)]);function *flatten7(arr) {let stack = arr.slice()while (stack.length) {const item = stack.shift()if(item.constructor === Array) {stack = stack.concat(item) //stack.push(...item)} else {yield item}}}console.log('flatten7', [...flatten7(arr2)]);