inp=[1,0,1,1,0,0,1,1]
n=len(inp)
lohash=[-1]*2*n+[-1]
hihash=[-1]*2*n+[-1]
max=0
a=0
for i in range(0,n):
    if inp[i]==1:
        a=a+1
    else:
        a=a-1
    if a==0:
        lohash[a+n]=hihash[a+n]=a
        if i+1>max:
             max=i+1
    else:
        if lohash[a+n]==-1:
            lohash[a+n]=i
        else:
            hihash[a+n]=i
            if (hihash[a+n]-lohash[a+n])>max:
                max=hihash[a+n]-lohash[a+n]
print max

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