When data is transmitted across a noisy channel,info can be lost during the transmission ,for ex-A message that is sent through a noisy channel as

"WHO PARKED ON HARRY'S POTTER SPOT?_" could be revised as the message

"HOP ON POP_" i.e, some character could be lost during transmission,

so that only a selected portion of the original message is received.

We can model the phenomena using character string

X=x1,x2,x3.....xn,we say that a string

Y=y1,y2,y3.....ym,is a sub-sequence of X if there are set of in-dices

{i1,i2,i3...ik..in},such that y1=xi1, y2=xi2 .......yk=xik and ij

for j=1 transcription of a received message is indeed a sub-sequence

of the message set.Therefore describe an O(n+m) time method for

determining if the given string Y of length m is a sub-sequence of a

given X of length n.