每日一算（日更）

摘要：每天练习一点点，每天收获一点点算法题收集网络，仅供学习参考字符串重复次数字符串重复次数统计字符重复出现的个数过滤对象数组中指定的对象过滤对象数组中指定的对象过滤方法数组递归实现过滤指定项数组递归实现过滤指定项测试数据过滤方法数组交集补集数组

每天练习一点点，每天收获一点点！！（算法题收集网络，仅供学习参考）

字符串重复次数

var str = "abcdeacdbe"; //统计字符重复出现的个数；

function findRepeatNum(str) {
    return str.split("").reduce((pre,cur) => {
        if(cur in pre) {
            pre[cur] += 1;
        }else{
            pre[cur] = 1;
        }
        return pre;
    },{})
}
console.log(findRepeatNum(str)) //{a: 2, b: 2, c: 2, d: 2, e: 2}

过滤对象数组中指定的对象

var arr1 = [1,2];
var arr2 = [{id:1,name:"s"},{id:2,name:"ds"},{id:3,name:"gg"}]
//过滤方法
arr3 = arr2.filter((item) => !arr1.includes(item.id)); //[{id:3,name:"gg"}]

数组递归实现过滤指定项

//测试数据
var data = [{
    isextend:1,                                              
    vaL:0,
    children:[{
        isextend:1,
        vaL:1,
        children:[{
            isextend:0,
            vaL:4
        },{
            isextend:1,
            vaL:5
        }]
    },{
       isextend:1,
       vaL:2,
       children:[]
    },{
       isextend:1,
       vaL:3,
       children:[]
    }]
}]

//过滤方法
function deleteNode(arr, key,targetValue) {
    return arr.filter(function(item, i) {
        if (item.children) {
            item.children = deleteNode(item.children, key,targetValue)
        }
        return item[key] !== targetValue;
    })
}

console.log(deleteNode(data, "isextend",0))

数组交集补集

//测试数据（过滤isextend为0的项）
const a = [1, 2, 3, 4];
const b = [2, 3, 5, 6];

//过滤方法
function filterArr(arr1,arr2,type) {
    let diffArr = [];
    let sameArr = [];
    sameArr = arr1.filter(v => {
        return arr2.some(a => {
            return v == a
        })
    })
    let mergeArr = [...arr1,...arr2];
    diffArr = mergeArr.filter(v => {
        return !sameArr.includes(v)
    })
    if (type == "same") {
        return sameArr
    } else {
        return diffArr
    }
}

console.log(filterArr(a,b,"same")) // [2,3]
console.log(filterArr(a,b,"diff")) // [1,4,5,6]

获取当前日期前n天的日期

function getIntervalDate(days) {
    let arrDateKeys = [...Array(days).keys()];
    let result = arrDateKeys.map(v => {
    let TimeStampOneDay = 24*60*60*1000;
    let d = new Date(Date.now() - TimeStampOneDay*v);
    let str = `${d.getFullYear()}年${d.getMonth() + 1}月${d.getDate()}日`;
        return str
    })
    return result;
}
console.log(getIntervalDate(3)) // ["2019年6月3日", "2019年6月2日", "2019年6月1日"]

计算数组中的最大差值

var arr = [1,3,5,7,9,0,11,14,8,6]; //在一个整数数组中，一个数字减去它左边的数字得到一个差值，求最大差值的数字

function findMaxDiffValue(arr) {
    var minValue = arr[0];
    var MaxDiffValue = 0;
    arr.forEach((v,index) => {
        if(minValue > v) minValue = v;
        var diff = v-minValue;
        if(diff > MaxDiffValue) MaxDiffValue = diff;
    })
    return MaxDiffValue
}
console.log(findMaxDiffValue(arr)) //14

对数组中重复对象进行操作

//数据样例
var arr = [
    { time: "20190807", cabin: "w",  dcp: 37 },
    { time: "20190806", cabin: "w",  dcp: 37 },
    { time: "20190805", cabin: "a",  dcp: 37 },
    { time: "20190806", cabin: "w",  dcp: 37 },
    { time: "20190807", cabin: "w",  dcp: 37 },
    { time: "20190804", cabin: "w",  dcp: 37 },
    { time: "20190803", cabin: "w",  dcp: 37 },
    { time: "20190805", cabin: "w",  dcp: 37 },
    { time: "20190802", cabin: "w",  dcp: 37 },
    { time: "20190806", cabin: "j",  dcp: 37 }, 
] 
//如果time，cabin相同，那么dcp字段的数值就相加,并且把cabin字段的value取出来变为一个新的字段加入当前对象，值为累加次数;
  
function filterArr(arr) {
    return arr.reduce((pre,cur,index) => {
        let {time,cabin,dcp} = cur;
        let isHas = pre.findIndex(v => v.time == time && v.cabin == cabin);
        if(isHas > -1){
            let cur = pre[isHas];
            cur["dcp"] += cur["dcp"];
            cur[cabin]++;
        }else{
            let clone = {...cur,[cabin]:1};
            pre.push(clone)
        }    
        return pre;
    },[])
}