我如何减少此代码的时间复杂度

Question

 let arr = [[{x: 1},{y: 2}],[{z: 3}]] let objs = [] arr.forEach(innerArray => { innerArray.forEach(obj => { objs.push(obj) }) }) console.log(objs) // [{x:1}, {y:2},{z:3}] 

I don't want to map array two time, could you please help me to find the better way of doing this.

Answer 1

You can use Array.prototype.flat()

Note: All the methods below are just alternative which will have high speed. Your solution has O(n) time-complexity and all the method below have same time-complexity. The time-complexity of merging two arrays is O(n) not O(1)

 let arr = [[{x: 1},{y: 2}],[{z: 3}]] let objs = arr.flat(); console.log(objs) 

Or another way is using concat() and reduce()

 let arr = [[{x: 1},{y: 2}],[{z: 3}]] let objs = arr.reduce((ac,a) => ac.concat(a),[]) console.log(objs) 

A better idea suggested in comments is using apply()

 let arr = [[{x: 1},{y: 2}],[{z: 3}]] let objs = [].concat.apply([], arr) console.log(objs)