Given an integer k and a string s, find the length of the longest substring that contains at most k distinct characters.

Daily_coding_Problem_13.py

'''
For example, given s = "abcba" and k = 2, the longest substring with k distinct characters is "bcb".
'''

def long_substr(s,k):
    long_st=0
    has_found=0
    dq=[]
    mapp=dict()
    for i,ch in enumerate(s):
        if(mapp.get(ch,-1) is -1):
            mapp[ch]=1
            dq.append(i)
        else:
            mapp[ch]+=1
            dq.append(i)
        if(len(mapp)>k):
            mapp[s[dq[0]]]-=1
            if(mapp[s[dq[0]]]==0):
                del mapp[s[dq[0]]]
            dq.pop(0)
        if(len(mapp)==k):
            long_st=max(long_st,dq[-1]-dq[0]+1)
        
    if long_st==0:
        return -1
    else:
        return long_st