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View Code? Open in Web Editor NEW日常收集一些练习题
日常收集一些练习题
function lastPromise(promiseFn) {
let resetReturn;
return function () {
let cancel = false;
if (resetReturn) resetReturn();
resetReturn = () => cancel = true
return new Promise((resolve) => {
promiseFn().then((res) => !cancel && resolve(res))
})
}
}
let count = 1
let fn = () => new Promise(rs => setTimeout(() => rs(count++)))
let lastGn = lastPromise(fn)
lastGn().then(console.log)
lastGn().then(console.log)
lastGn().then(console.log)
function usePrevious(value) {
const ref = useRef()
useEffect(() => {
ref.current = value
}, [value])
return ref.current
}
function myFlat(arr) {
let result = [];
for(let i = 0; i < arr.length; i++) {
if (Array.isArray(arr[i])) result = result.concat(myFlat(arr[i]))
else result = result.concat(arr[i])
}
return result;
}
function myFlat(arr) {
return arr.reduce((p, n) => p.concat(Array.isArray(n) ? myFlat(n) : n), []);
}
以下数据结构中,id 代表部门编号,name 是部门名称,parentId 是父部门编号,
为 0 代表一级部门,现在要求实现一个 convert 方法,
把原始 list 转换成树形结构,parentId 为多少就挂载在该 id 的属性 children 数组下,结构如下:
// 原始 list 如下
let list =[
{id:1,name:'部门A',parentId:0},
{id:2,name:'部门B',parentId:0},
{id:3,name:'部门C',parentId:1},
{id:4,name:'部门D',parentId:1},
{id:5,name:'部门E',parentId:2},
{id:6,name:'部门F',parentId:3},
{id:7,name:'部门G',parentId:2},
{id:8,name:'部门H',parentId:4}
];
const result = convert(list, ...);
// 转换后的结果如下
let result = [
{
id: 1,
name: '部门A',
parentId: 0,
children: [
{
id: 3,
name: '部门C',
parentId: 1,
children: [
{
id: 6,
name: '部门F',
parentId: 3
}, {
id: 16,
name: '部门L',
parentId: 3
}
]
},
{
id: 4,
name: '部门D',
parentId: 1,
children: [
{
id: 8,
name: '部门H',
parentId: 4
}
]
}
]
},
···
];
let len = list.length;
for (let i = len - 1; i >= 0; i--) {
let item = list[i];
let parentId = item.parentId;
if (list[parentId - 1]) {
if (list[parentId - 1].children) {
list[parentId - 1].children.push(list[i]);
} else list[parentId - 1].children = [list[i]];
list.splice(i, 1);
}
}
//输入以下有序的list数组
var list = [
'h3',
'h2', 'h3',
'h1', 'h2', 'h3', 'h3', 'h2', 'h3',
'h1', 'h2', 'h4', 'h2', 'h3',s
]
//输出以下树形数组结构
[
{
name: 'h3',
child: []
},
{
name: 'h2',
child: [{name: 'h3'}]
},
{
name: 'h1',
child: [
{
name: 'h2',
child: [{name: 'h3'}, {name: 'h3'}]
},
{
name: 'h2',
child: [{name: 'h3'}]
}
]
},
{
name: 'h1',
child: [
{
name: 'h2',
child: [{name: 'h4'}]
},
{
name: 'h2',
child: [{name: 'h3'}]
}
]
}
]
let stacks = [];
function createNode(key) {
return {
name: key,
child: []
}
}
function task(node, key) {
stacks.push({
name: key,
node: node
})
}
function Compare(k1, k2) {
return Number(k1.slice(1)) <= Number(k2.slice(1))
}
function insert(el) {
let _t = stacks[stacks.length - 1];
if (!stacks.length) {
let newnode = createNode(el);
result.push(newnode);
task(newnode, el);
} else {
if (Compare(el, _t.name)) {
stacks.pop();
insert(el)
} else {
let newnode = createNode(el);
_t.node.child.push(newnode);
task(newnode, el);
}
}
}
let list = []
let total = 1000000
for(let i = 0; i < total; i++) {
list.push('h' + Math.floor(Math.random() * 10 + 1))
}
let result = []
list.forEach(insert);
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