Meeting Rooms or No Of Platforms No Of Party Halls

#Function to find the minimum number of platforms required at the
    #railway station such that no train waits.
def minimumPlatform(n,arr,dep):
    i=0
    j=0
    arr.sort()
    dep.sort()
    res=pf=0
    while i<n     and j<n:
        if arr[i]<=dep[j]:
            i=i+1
            pf+=1
            res=max(pf,res)
        else:
            j=j+1
            pf-=1
            return res