Some front-end algorithms (common sorting, multidimensional array flattening, tree traversal)

One: Common sorting algorithm

Bubble Sort:

function bubbleSort(arr) {
    var len = arr.length;
    for (var i = 0; i < len; i++) {
        for (var j = 0; j < len - 1 - i; j++) {
            if (arr[j] > arr[j+1]) {        //相邻元素两两对比
                var temp = arr[j+1];        //元素交换
                arr[j+1] = arr[j];
                arr[j] = temp;
            }
        }
    }
    return arr;
}

Quick sort:

let quickSort = function(arr) {
　　if (arr.length <= 1) { return arr; }
　　let pivotIndex = Math.floor(arr.length / 2);
　　let pivot = arr.splice(pivotIndex, 1)[0];
　　let left = [];
　　let right = [];
　　for (let i = 0; i < arr.length; i++){
　　　　if (arr[i] < pivot)  {
　　　　　　left.push(arr[i]);
　　　　} else {
　　　　　　right.push(arr[i]);
　　　　}
　　}
　　return quickSort(left).concat([pivot], quickSort(right));
}

Two: Array de-duplication

es6 Set de-duplication

function distinct(arr){
	return Array.from(new Set(arr))
}

Three: array flattening

Recursion:

function flatten(arr){
    let res = [];
    for(let i = 0; i < arr.length; i++){
        if(Array.isArray(arr[i])){
            res = res.concat(flatten(arr[i]));
        }else{
            res.push(arr[i]);
        }
    }
    return res;
}

reduce

function flatten(arr){
    return arr.reduce(function(prev,item){
        return prev.concat(Array.isArray(item)?flatten(item):item);
    },[]);
}

function flatten(arr){
    return arr.toString().split(',').map(function(item){
        return item;
    })
}

Tree traversal

Depth-first traversal

function deepTraversal(node){
    let nodes=[];
    if(node!=null){
        nodes.push[node];
        let childrens=node.children;
        for(let i=0;i<childrens.length;i++)
            deepTraversal(childrens[i]);
    }
    return nodes;
}

Breadth first traversal

function wideTraversal(node){
    let nodes=[],i=0;
    if(node!=null){
        nodes.push(node);
        wideTraversal(node.nextElementSibling);
        node=nodes[i++];
        wideTraversal(node.firstElementChild);
    }
    return nodes;
}