排序算法
1、冒泡排序
function bubbleSort(arr){
var i = j = 0;
for(i=1; i<arr.length; i++){
for(j=0; j<=arr.length-i; j++){
var temp = 0;
if(arr[j] > arr[j+1]){ // ">" 從小到大排序 "<" 從大到小排序
temp = arr[j]
arr[j] = arr[j+1]
arr[j+1] = temp
}
}
}
return arr
}
2、快速排序
function quickSort(arr,l,r){
if(l < r){
var i = l, j = r, x = arr[i];
while(i<j){
while(i<j && arr[j]>x)
j--;
if(i<j)
arr[i++] = arr[j];
while(i<j && arr[i]<x)
i++;
if(i<j)
arr[j--] = arr[i];
}
arr[i] = x;
quickSort(arr, l, i-1);
quickSort(arr, i+1, r);
}
}
3、二路歸并
function merge(left, right) {
var result = [],
il = 0,
ir = 0;
while (il < left.length && ir < right.length) {
if (left[il] < right[ir]) {
result.push(left[il++]);
} else {
result.push(right[ir++]);
}
}
while(left[il]){
result.push(left[il++]);
}
while(right[ir]){
result.push(right[ir++]);
}
return result;
}
字符串操作
1、判斷回文字符串
function palindrome(str){
// \W匹配任何非單詞字符。等價于“[^A-Za-z0-9_]”。
var re = /[\W_]/g;
// 將字符串變成小寫字符,并干掉除字母數字外的字符
var lowRegStr = str.toLowerCase().replace(re,'');
// 如果字符串lowRegStr的length長度為0時，字符串即是palindrome
if(lowRegStr.length===0) return true;
// 如果字符串的第一個和最后一個字符不相同，那么字符串就不是palindrome
if(lowRegStr[0]!=lowRegStr[lowRegStr.length-1]) return false;
//遞歸
return palindrome(lowRegStr.slice(1,lowRegStr.length-1));
}
2、翻轉字符串
思路一：反向遍歷字符串
function reverseString(str){
var tmp = '';
for(var i=str.length-1; i>=0; i--)
tmp += str[i];
return tmp
}
思路二：轉化成array操作
function reverseString(str){
var arr = str.split("");
var i = 0,j = arr.length-1;
while(i<j){
tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
i++;
j--;
}
return arr.join("");
}
3、生成指定長度隨機字符串
function randomString(n){
var str = 'abcdefghijklmnopqrstuvwxyz0123456789';
var tmp = '';
for(var i=0; i<n; i++) {
tmp += str.charAt(Math.round(Math.random()*str.length));
}
return tmp;
}
4、統計字符串中次數最多字母
function findMaxDuplicateChar(str) {
if(str.length == 1) {
return str;
}
var charObj = {};
for(var i = 0; i < str.length; i++) {
if(!charObj[str.charAt(i)]) {
charObj[str.charAt(i)] = 1;
} else {
charObj[str.charAt(i)] += 1;
}
}
var maxChar = '',
maxValue = 1;
for(var k in charObj) {
if(charObj[k] >= maxValue) {
maxChar = k;
maxValue = charObj[k];
}
}
return maxChar + '：' + maxValue;
}
數組操作
1、數組去重
function unique(arr){
var obj = {}
var result = []
for(var i in arr){
if(!obj[arr[i]]){
obj[arr[i]] = true;
result.push(arr[i]);
}
}
return result;
}
2、數組中最大差值
function getMaxProfit(arr){
var min = arr[0],
max = arr[0];
for(var i = 0; i < arr.length; i++){
if(arr[i] < min) min = arr[i];
if(arr[i] > max) max = arr[i];
}
return max - min;
}
3、無形參數組排序
function mySort() {
var tags;
tags = Array.prototype.slice.call(arguments);
var temp;
for (var i = 0; i < tags.length; i++) {
for (var j = 0; j < tags.length - i; j++) {
if (tags[j] > tags[j + 1]) {
temp = tags[j];
tags[j] = tags[j + 1];
tags[j + 1] = temp;
}
}
}
return tags;
}
其他常見算法
1、階乘
非遞歸實現
function factorialize(num) {
var result = 1;
if(num < 0) return -1;
if(num == 0 || num == 1) return 1;
while(num>1) {
result *= num--;
}
return result;
}
遞歸實現
function factorialize(num) {
var result = 1;
if(num < 0) return -1;
if(num == 0 || num == 1) return 1;
if(num > 1) return num*factorialize(num-1);
}
2、生成菲波那切數列
強行遞歸實現
function getfib(n){
if(n == 0) return 0;
if(n == 1) return 1;
if(n > 1) return getfib(n-1) + getfib(n-2);
}
function fibo(len){
var fibo = [];
for(var i = 0; i < len; i++){
fibo.push(getfib(i));
}
return fibo;
}
簡約非遞歸實現
function getFibonacci(n) {
var fibarr = [];
var i = 0;
while(i < n) {
if(i <= 1) {
fibarr.push(i);
} else {
fibarr.push(fibarr[i - 1] + fibarr[i - 2])
}
i++;
}
return fibarr;
}
3、二分查找
非遞歸實現
function binary_search(arr, key) {
var low = 0,
high = arr.length - 1;
while(low <= high){
var mid = parseInt((high + low) / 2);
if(key == arr[mid]){
return mid;
}else if(key > arr[mid]){
low = mid + 1;
}else if(key < arr[mid]){
high = mid -1;
}
}
return -1;
}
遞歸實現
function binary_search2(arr, low, high, key) {
if(low > high) return -1;
var mid = parseInt((low + high)/2);
if(key == arr[mid]) {
return mid;
} else if(key > arr[mid]) {
return binary_search2(arr, mid+1, high, key);
} else if(key < arr[mid]) {
return binary_search2(arr, low, mid-1, key);
}
}
