1. 统计一个字符串出现频率最高的字母/数字
let str = 'asdfghjklaqwertyuiopiaia';
const strChar = str => {
let string = [...str],
maxValue = '',
obj = {},
max = 0;
string.forEach(value => {
obj[value] = obj[value] == undefined ? 1 : obj[value] + 1
if (obj[value] > max) {
max = obj[value]
maxValue = value
}
})
return maxValue;
}
console.log(strChar(str)) // a
2. 数组去重
1.forEach
let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr => {
let obj = {}
arr.forEach(value => {
obj[value] = 0
})
return Object.keys(obj)
}
console.log(unique(arr)) // ['1','2','3','a','b']
2. filter
let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr => {
return arr.filter((ele, index, array) => {
return index === array.indexOf(ele)
})
}
console.log(unique(arr)) // ['1','2','3','a','b']
3. set
let arr = ['1', '2', '3', '1', 'a', 'b', 'b']
const unique = arr => {
return [...new Set(arr)]
}
console.log(unique(arr)) // ['1','2','3','a','b']
3. 翻转字符串
let str ="Hello Dog";
const reverseString = str =>{
return [...str].reverse().join("");
}
console.log(reverseString(str)) // goD olleH
4. 数组中最大差值
1. forEach
let arr = [23, 4, 5, 2, 4, 5, 6, 6, 71, -3];
const difference = arr => {
let min = arr[0],
max = 0;
arr.forEach(value => {
if (value < min) min = value
if (value > max) max = value
})
return max - min ;
}
console.log(difference(arr)) // 74
2. max、min
let arr = [23, 4, 5, 2, 4, 5, 6, 6, 71, -3];
const difference = arr => {
let max = Math.max(...arr),
min = Math.min(...arr);
return max - min ;
}
console.log(difference(arr)) // 74
5. 不借助临时变量，进行两个整数的交换
1. 数组解构
let a = 2,
b = 3;
[b,a] = [a,b]
console.log(a,b) // 3 2
let arr = [23, 4, 5, 2, 4, 5, 6, 6, 71, -3];
console.log(difference(arr)) // 74
2. 算术运算（加减）
// 输入a = 2,b = 3,输出 a = 3,b = 2
let a = 2,
b = 3;
const swop = (a, b) => {
b = b - a;
a = a + b;
b = a - b;
return [a,b];
}
console.log(swop(2,3)) // [3,2]
3. 逻辑运算（异或）
let a = 2,
b = 3;
const swop = (a, b) => {
a ^= b; //x先存x和y两者的信息
b ^= a; //保持x不变，利用x异或反转y的原始值使其等于x的原始值
a ^= b; //保持y不变，利用x异或反转y的原始值使其等于y的原始值
return [a,b];
}
console.log(swop(2,3)) // [3,2]
6. 排序 (从小到大)
1.冒泡排序
let arr = [43, 32, 1, 5, 9, 22];
const sort = arr => {
let res = []
arr.forEach((v, i) => {
for (let j = i + 1; j < arr.length; j++) {
if (arr[i] > arr[j]) {
[arr[i],arr[j]] = [arr[j],arr[i]]
}
}
})
return arr
}
console.log(sort(arr)) // [1, 5, 9, 22, 32, 43]
7. 比较
1. 比较两个数组的内容是否相同
// Warn if overriding existing method
if (Array.prototype.equals)
console.warn(
"Overriding existing Array.prototype.equals. Possible causes: New API defines the method, there's a framework conflict or you've got double inclusions in your code.");
// attach the .equals method to Array's prototype to call it on any array
Array.prototype.equals = function (array) {
// if the other array is a falsy value, return
if (!array)
return false;
// compare lengths - can save a lot of time
if (this.length != array.length)
return false;
for (var i = 0, l = this.length; i < l; i++) {
// Check if we have nested arrays
if (this[i] instanceof Array && array[i] instanceof Array) {
// recurse into the nested arrays
if (!this[i].equals(array[i]))
return false;
} else if (this[i] != array[i]) {
// Warning - two different object instances will never be equal: {x:20} != {x:20}
return false;
}
}
return true;
}
// Hide method from for-in loops
Object.defineProperty(Array.prototype, "equals", {
enumerable: false
});
2. 比较Object
Object.prototype.equals = function (object2) {
//For the first loop, we only check for types
for (propName in this) {
//Check for inherited methods and properties - like .equals itself
//https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty
//Return false if the return value is different
if (this.hasOwnProperty(propName) != object2.hasOwnProperty(propName)) {
return false;
}
//Check instance type
else if (typeof this[propName] != typeof object2[propName]) {
//Different types => not equal
return false;
}
}
//Now a deeper check using other objects property names
for (propName in object2) {
//We must check instances anyway, there may be a property that only exists in object2
//I wonder, if remembering the checked values from the first loop would be faster or not
if (this.hasOwnProperty(propName) != object2.hasOwnProperty(propName)) {
return false;
} else if (typeof this[propName] != typeof object2[propName]) {
return false;
}
//If the property is inherited, do not check any more (it must be equa if both objects inherit it)
if (!this.hasOwnProperty(propName))
continue;
//Now the detail check and recursion
//This returns the script back to the array comparing
/**REQUIRES Array.equals**/
if (this[propName] instanceof Array && object2[propName] instanceof Array) {
// recurse into the nested arrays
if (!this[propName].equals(object2[propName]))
return false;
} else if (this[propName] instanceof Object && object2[propName] instanceof Object) {
// recurse into another objects
//console.log("Recursing to compare ", this[propName],"with",object2[propName], " both named \""+propName+"\"");
if (!this[propName].equals(object2[propName]))
return false;
}
//Normal value comparison for strings and numbers
else if (this[propName] != object2[propName]) {
return false;
}
}
//If everything passed, let's say YES
return true;
}
8. 随机数生成
1. min ≤ r ≤ max
function RandomNumBoth(Min,Max){
var Range = Max - Min;
var Rand = Math.random();
var num = Min + Math.round(Rand * Range); //四舍五入
return num;
}
2. min ≤ r < max
function RandomNum(Min, Max) {
var Range = Max - Min;
var Rand = Math.random();
var num = Min + Math.floor(Rand * Range); //舍去
return num;
}
3. min < r ≤ max
function RandomNum(Min, Max) {
var Range = Max - Min;
var Rand = Math.random();
if(Math.round(Rand * Range)==0){
return Min + 1;
}
var num = Min + Math.round(Rand * Range);
return num;
}
4. min < r < max
function RandomNum(Min, Max) {
var Range = Max - Min;
var Rand = Math.random();
if(Math.round(Rand * Range)==0){
return Min + 1;
}else if(Math.round(Rand * Max)==Max)
{
index++;
return Max - 1;
}else{
var num = Min + Math.round(Rand * Range) - 1;
return num;
}
}
