【前端面试】七、算法-数组展平

1.判断数组

javascript 复制代码

    // 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

javascript 复制代码

    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

javascript 复制代码

    // 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

javascript 复制代码

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

循环

javascript 复制代码

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

栈的思想

javascript 复制代码

    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

javascript 复制代码

    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)]);