js常见算法(一)：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，获取地址连接的各个参数

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，获取地址连接的各个参数

之后会记录本身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。

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);
复制代码

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);
复制代码

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);
复制代码

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);
复制代码

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);
复制代码

6. 利用splice直接在原数组进行操做

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);
复制代码

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);
复制代码

// 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，获取地址连接的各个参数
复制代码

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);
复制代码

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);
复制代码

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);
复制代码

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);
复制代码

获取地址连接的各个参数

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);
复制代码

es6 实践

var arr = [1,2,3,4,5];
const param = arr.find(it => it === 5);
param += 1;
console.log(arr);
复制代码