javascript--Interview--algorithm--string-3

Problem Description: The simplest string compression is achieved by using the number of occurrences of a character in a string, the string is not shortened after compression, and the original string is returned.

For example Abbbcccccddef, after compression for ab3c5d2ef; The string is large enough (greater than 10 million characters), consider the efficiency problem;

functioncompress_str (str) {varTmp_char = Str.charat (0); varCount = 1; varTmp_str = ' '; varindex = 0;  for(varI=1; i<=str.length; i++){        if(!str.charat (i) | | Str.charat (i)! =Tmp_char) {Tmp_str= Tmp_str + Tmp_char + (Count > 1? Count: "); Tmp_char=Str.charat (i); Count= 1; Index++; } Else{Count++; }    }    if(index = = str.length)returnstr; returntmp_str;}varstr1 = ' ABCDEDF '; Console.log (str1+ ' compressed is ' +compress_str (str1));varstr2 = ' abbbcccccddefbbb '; Console.log (str2+ ' compressed is ' + compress_str (str2));

In JS, once the string has been assigned, it cannot be modified.
Look at the string connection operation based on this background:

var= ' This is a string '= str + ', another string. ';

The processing mechanism for this connection operation JS is: Create a new temporary string, assign the new string to STR + ', another string. ', and then return the new string and destroy the original string at the same time. Therefore, the connection efficiency of the string is low. The way to improve efficiency is to use the Join function of the array

var temparr == ' This is a string '; Temparr.push (SRC); Temparr.push (', another string. '  = Temparr.join (");

However, in the advanced programming of JavaScript, it is also mentioned that:
This process occurs in the background, and this is why it is very slow to stitch strings in some older browsers, such as Firefox, IE6, and so on, which have a version of less than 1.0. But later versions of these browsers have solved this problem.
As a result, efficiency gains are only available in low-version browsers such as IE6.

Therefore, in order to improve efficiency, we need to make further changes, we use string arrays instead of string concatenation

functioncompress_str_2 (str) {varTmp_char = Str.charat (0); varCount = 1; varTmp_arr =NewArray (); varindex = 0;  for(varI=1; i<=str.length; i++){        if(!str.charat (i) | | Str.charat (i)! =Tmp_char) {Tmp_arr.push (Tmp_char)if(Count > 1) Tmp_arr.push (count); Tmp_char=Str.charat (i); Count= 1; Index++; } Else{Count++; }    }    if(index = = str.length)returnstr; returnTmp_arr.join (' ');}varstr1 = ' ABCDEDF '; Console.log (str1+ ' compressed is ' +compress_str_2 (str1));varstr2 = ' abbbcccccddefbbb '; Console.log (str2+ ' compressed is ' + compress_str_2 (str2));

javascript--Interview--algorithm--string-3