摘要：每天練習一點點，每天收獲一點點算法題收集網絡，僅供學習參考字符串重復次數字符串重復次數統計字符重復出現的個數過濾對象數組中指定的對象過濾對象數組中指定的對象過濾方法數組遞歸實現過濾指定項數組遞歸實現過濾指定項測試數據過濾方法數組交集補集數組

每天練習一點點，每天收獲一點點！！（算法題收集網絡，僅供學習參考）

字符串重復次數

var str = "abcdeacdbe"; //統計字符重復出現的個數；

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}

過濾對象數組中指定的對象

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

數組遞歸實現過濾指定項

//測試數據
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:[]
    }]
}]

//過濾方法
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))

數組交集補集

//測試數據（過濾isextend為0的項）
const a = [1, 2, 3, 4];
const b = [2, 3, 5, 6];

//過濾方法
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]

獲取當前日期前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"]

計算數組中的最大差值

var arr = [1,3,5,7,9,0,11,14,8,6]; //在一個整數數組中，一個數字減去它左邊的數字得到一個差值，求最大差值的數字

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

對數組中重復對象進行操作

//數據樣例
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字段的數值就相加,并且把cabin字段的value取出來變為一個新的字段加入當前對象，值為累加次數;
  
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;
    },[])
}