Run-length encoding

Run-length encoding (RLE) is a very simple form of data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run. Wikipedia

Task

Your task is to write such a run-length encoding. For a given string, return a list (or array) of pairs (or arrays) [ (i1, s1), (i2, s2), …, (in, sn) ], such that one can reconstruct the original string by replicating the character sx ix times and concatening all those strings. Your run-length encoding should be minimal, ie. for all i the values si and si+1 should differ.

Examples

As the article states, RLE is a very simple form of data compression. It's only suitable for runs of data, as one can see in the following example:

run_length_encoding("hello world!")
 //=>      [[1,'h'], [1,'e'], [2,'l'], [1,'o'], [1,' '], [1,'w'], [1,'o'], [1,'r'], [1,'l'], [1,'d'], [1,'!']]

It's very effective if the same data value occurs in many consecutive data elements:

run_length_encoding("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbb")
# => [[34,'a'], [3,'b']]

---

def run_length_encoding(s):
    if s=="":
        return []
    rep=0
    cur=s[0]
    templist=[]
    ans=[]
    for i in s:
        if i == cur:
            rep+=1
        else:
            templist.append(rep)
            templist.append(cur)
            ans.append(templist)
            templist=[]
            cur=i
            rep=1
    templist.append(rep)
    templist.append(cur)
    ans.append(templist)
    templist=[]
    return ans