出现次数最多的字符

javascript面试题
javascript
  1. 问题：给定一个字符串，求出里面出现次数最多的字符。
  2. 输入：字符串
  3. 输出：{[字符]:[出现次数],…}
  4. 举例：输入：'hello world' 输出：{'l':3}

方法1:

先排序，然后单次遍历

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
function getMostAppear(str){
	if(str.length === 0) return {};
	var sortedArr = str.split('').sort(function(a, b){
		return a - b;
	});
	var len = sortedArr.length;
	
	// 用来记录最多的次数
	var max = 0;
	
	// 用来记录出现最多次数的字符
	var c = '';
	
	// 用来记录当前字符和次数的映射
	var currAppear = {};
	for(var i = 0; i < len; i++){
		var currChar = sortedArr[i];
		if(!currAppear[currChar]){
			currAppear[currChar] = 1;
		}else{
			currAppear[currChar]++;
		}
		if(currAppear[currChar] > max){
			max = currAppear[currChar];
			c = currChar;
		}
	}
	var mostAppear = {};
	mostAppear[c] = max;
	return mostAppear;
}

方法2:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
function getMostAppear(str){
	if(str.length === 0) return {};
	var len = str.length;
	
	// 用来记录最多的次数
	var max = 0;
	
	// 用来记录出现最多次数的字符
	var c = '';
	
	// 字符和出现次数的映射
	var charNumMap = {};
	
	for(var i = 0; i < len; i++){
		var curr = str.charAt(i);
		if(!charNumMap[curr]){
			charNumMap[curr] = 1;
		}else{
			charNumMap[curr]++;
		}
		
		if(charNumMap[curr] > max){
			max = charNumMap[curr];
			c = curr;
		}
	}
	
	var mostAppear = {};
	mostAppear[c] = max;
	return mostAppear;
}
评论

gulp的简介

javascriptgulp
javascript, gulp

什么是gulp

gulp是在你的开发过程中用来帮你自动化一些麻烦耗时的工作的工具集。比如在web开发过程中，它能帮你完成css预处理，js文件整合，压缩，实时重加载等等。并且它还和目前市场上主流的IDE整合，无论是在PHP,.NET,Node.js,Java等等开发者都很喜欢用它。拥有超过1700中插件，gulp能够让你从繁琐的构建系统中解脱出来，真正的开始干活。

怎样开始

  1. 安装Node.js
  2. 创建一个项目，比如说gulptest
  3. 在控制台项目路径下，npm init，跟着步骤创建package.json文件
  4. npm install –global gulp，使gulp命令可以在命令行中使用。
  5. npm install –save-dev gulp，在项目上安装gulp模块，同时将 gulp添加到package.json的dev-dependencies依赖中。
  6. 比如我们需要压缩css文件，先安装需要的模块npm install –save-dev gulp-minify-css

  7. 在项目路径下创建gulpfile.js

    var gulp = require('gulp');
var minifyCss = require('gulp-minify-css');

gulp.task('minify-css', function() {
  return gulp.src('styles/*.css')
    .pipe(minifyCss({compatibility: 'ie8'}))
    .pipe(gulp.dest('dist'));
   });

  8. 运行gulp minify-css命令

gulp API

跳转到：gulp.src | gulp.dest | gulp.task |gulp.watch

gulp.src

  • Emits files matching provided glob or an array of globs. Returns a stream of Vinyl files that can be piped to plugins.

    gulp.src('client/templates/*.jade')
      .pipe(jade())
     .pipe(minify())
      .pipe(gulp.dest('build/minified_templates'));

  • 根据路径找到文件然后把它放在流里面pipe到gulp插件

    gulp.src('client/js/**/*.js') // Matches 'client/js/somedir/somefile.js' and resolves `base` to `client/js/`
      .pipe(minify())
      .pipe(gulp.dest('build'));  // Writes 'build/somedir/somefile.js'

gulp.src('client/js/**/*.js', { base: 'client' })
      .pipe(minify())
      .pipe(gulp.dest('build'));  // Writes 'build/js/somedir/somefile.js'

gulp.dest

  • Can be piped to and it will write files. Re-emits all data passed to it so you can pipe to multiple folders. Folders that don’t exist will be created.

    gulp.src('./client/templates/*.jade')
      .pipe(jade())
      .pipe(gulp.dest('./build/templates'))
     .pipe(minify())
      .pipe(gulp.dest('./build/minified_templates'));

gulp.task

  • Define a task using Orchestrator.

    gulp.task('somename', function() {
      // Do stuff
});

  • An array of tasks to be executed and completed before your task will run.

    gulp.task('mytask', ['array', 'of', 'task', 'names'], function() {
      // Do stuff
});

  • You can also omit the function if you only want to run the dependency tasks:

    gulp.task('build', ['array', 'of', 'task', 'names']);

  • Accept a callback

    // run a command in a shell
var exec = require('child_process').exec;
gulp.task('jekyll', function(cb) {
     // build Jekyll
     exec('jekyll build', function(err) {
       if (err) return cb(err); // return error
    cb(); // finished task
      });
});

  • Return a stream

    gulp.task('somename', function() {
     var stream = gulp.src('client/**/*.js')
        .pipe(minify())
        .pipe(gulp.dest('build'));
      return stream;
});

  • Return a promise

    var Q = require('q');

gulp.task('somename', function() {
      var deferred = Q.defer();

      // do async stuff
      setTimeout(function() {
        deferred.resolve();
      }, 1);

      return deferred.promise;
});

  • 默认情况下task中的任务是同步进行的，所以，如果需要在保证某一项任务在其他之前可以按照如下操作：

    var gulp = require('gulp');

// takes in a callback so the engine knows when it'll be done
gulp.task('one', function(cb) {
// do stuff -- async or otherwise
cb(err); // if err is not null and not undefined, the run will stop, and note that it failed
});

// identifies a dependent task must be complete before this one begins
gulp.task('two', ['one'], function() {
    // task 'one' is done now
});

gulp.task('default', ['one', 'two']);

    gulp.watch

  • Watch files and do something when a file changes. This always returns an EventEmitter that emits change events.

  • Names of task(s) to run when a file changes, added with gulp.task()

    var watcher = gulp.watch('js/**/*.js', ['uglify','reload']);
watcher.on('change', function(event) {
      console.log('File ' + event.path + ' was ' + event.type + ', running tasks...');
});

常用的gulp plugins

  1. 编译Sass gulp-ruby-sass
  2. 自动添加前缀 gulp-autoprefixer
  3. 压缩CSS gulp-minify-css
  4. JSHint gulp-jshint
  5. Concatenation gulp-concat
  6. Uglify gulp-uglify
  7. 图片压缩 gulp-imagemin
  8. 实时重加载 gulp-livereload
  9. 图片缓存从而只压缩改变的图片 gulp-cache
  10. Notify of changes gulp-notify
  11. 清除文件干净地构建 del

参考链接：

  1. github-gulp
  2. gulp-documentation
评论