js常见算法(一)：排序，数组去重，打乱数组，统计数组各个元素出现的次数， 字符串各个字符的出现次数

摘要：排序，数组去重，打乱数组，统计数组各个元素出现的次数，字符串各个字符的出现次数，获取地址链接的各个参数以后会记录自己解决过和遇到过的算法相关的题，系列一就以常见的开篇吧。

以后会记录自己解决过和遇到过的算法相关的题，系列一就以常见的开篇吧。

本来想多列几个排序方法，但是其它都不常见，更多请点击查看，冒泡排序和快速排序中以快速排序最优。

var arr = [0, 4, 2, 1, 3];
var i = j = 0;
for(i; i" 从小到大排序
        // "<" 从大到小排序
        if(arr[j] > arr[j+1]){
            temp = arr[j]
            arr[j] = arr[j+1]
            arr[j+1] = temp
        }
    }
}

console.log(arr);

function quickSort(arr){
    //如果数组<=1,则直接返回
    if (arr.length <= 1) { return arr; }
    var pivotIndex = Math.floor(arr.length/2);
    //找基准，并把基准从原数组删除
    var pivot = arr.splice(pivotIndex,1)[0];
    //定义左右数组
    var left = [];
    var right = [];

    //比基准小的放在left，比基准大的放在right
    for (var i=0;i
数组去重
1. 遍历数组法
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
for (var i = 0, newArr = [], len = arr.length; i < len; i++){
    if (newArr.indexOf(arr[i]) == -1) {
        newArr.push(arr[i]);
    }
}
console.log(newArr);
2. 数组下标判断法
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
for (var i = 1, newArr = [arr[0]], len = arr.length; i < len; i++){
    if (arr.indexOf(arr[i]) == i) {
        newArr.push(arr[i]);
    }
}
console.log(newArr);
3. 对象键值对法
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
for (var i = 0, obj = {}, newArr = [], len = arr.length, val, type; i < len; i++){
    val = arr[i];
    type = typeof val;
    if (!obj[val]) {  // 对象没有该键对应的值
        obj[val] = type;
        newArr.push(val);
    } else if (obj[val].indexOf(type) < 0) {//对象有该键对应的值且它的值是不重复的
        obj[val] = type;
        newArr.push(val);
    }
}
console.log(newArr);
4. 排序后相邻去除法
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
arr.sort();
var newArr = [arr[0]];
for (var i = 1, len = arr.length; i < len; i++) {
    if (arr[i] !== newArr[newArr.length-1]) {
        newArr.push(arr[i]);
    }
}
console.log(newArr);
5. 优化遍历数组法
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
for (var i = 0, len = arr.length, newArr = []; i < len; i++) {
    for (var j = i + 1; j < len; j++) {
        if (arr[i] === arr[j]) j = ++i;
    }
    newArr.push(arr[i]);
}
console.log(newArr);
6. 利用splice直接在原数组进行操作
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
for (var i = 0, len = arr.length; i < len; i++) {
    for (var j = i + 1; j < len; j++) {
        if (arr[i] === arr[j]) {
            arr.splice(j, 1);
            len--;
            j--;
        }
    }
}
console.log(arr);
7. es6简化版
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
// 7.1
var newArr = [...new Set(arr)]; 
console.log(newArr);

// 7.2
var newArr = Array.from(new Set(arr));
console.log(newArr);
// 数组去重，打乱数组，统计数组各个元素出现的次数， 字符串各个字符的出现次数，获取地址链接的各个参数

打乱数组
var arr = [2,5,"6",3,9,"2",4,7];
arr.sort(function(){ return 0.5 - Math.random() });
console.log(arr);
统计数组各个元素出现的次数
1. 自创
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
for (var i = 0, len = arr.length, newArr = []; i < len; i++) {
    var isPush = true;
    for (var j = 0, l = newArr.length; j < l; j++) {
        if (arr[i] === newArr[j].val) {
            isPush = false;
            newArr[j].count++;
        }
    }
    if (isPush) {
        newArr.push({val: arr[i], count: 1});
    } else {
        isPush = true;
    }
}
console.log(newArr);
2. es6
var arr = ["2", 1, 5, 4, 7, "9", 4, 1, "2", 6, 8, 2];
var newArr = arr.reduce((arrs, cv) => {
    const found = arrs.find(it => it[0] === cv);
    if (found) {
        found[1] += 1;
    } else {
        arrs.push([cv, 1]);
    }
    return arrs;
}, []);
console.log(newArr);
字符串各个字符的出现次数
var str = "abdcsdwdaoprr";
for (var i = 0, len = str.length, obj = {}; i < len; i++) {
    if (obj[str[i]]) {
        obj[str[i]]++;
    } else {
        obj[str[i]] = 1;
    }
}
console.log(obj);
获取地址链接的各个参数
var url = "https://www.google.com.hk/search?safe=strict&ei=M_u5WvLZO4bzUrfpn_AJ&q=js%9F%&oq=js%E7%BB&gs_l=psy-ab";
var search = url.substring(url.indexOf("?")+1);
    var tmpArr = search.split("&");
    var urlParmObj = {};
    if (tmpArr.length > 0 && tmpArr[0] != "") {
            for (var i = 0, len = tmpArr.length; i < len; i++) {
                    var tmp = tmpArr[i].split("=");
                    urlParmObj[tmp[0]] = tmp[1];
            }
    }
    console.log(urlParmObj);
es6 实践
var arr = [1,2,3,4,5];
const param = arr.find(it => it === 5);
param += 1;
console.log(arr);
更多其它内容请查看