NHAY - A Needle in the Haystack

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Write a program that finds all occurences of a given pattern in a given input string. This is often referred to as finding a needle in a haystack.

The program has to detect all occurences of the needle in the haystack. It should take the needle and the haystack as input, and output the positions of each occurence, as shown below. The suggested implementation is the KMP algorithm, but this is not a requirement. However, a naive approach will probably exceed the time limit, whereas other algorithms are more complicated... The choice is yours.


The input consists of a number of test cases. Each test case is composed of three lines, containing:

  • the length of the needle,
  • the needle itself,
  • the haystack.

The length of the needle is only limited by the memory available to your program, so do not make any assumptions - instead, read the length and allocate memory as needed. The haystack is not limited in size, which implies that your program should not read the whole haystack at once. The KMP algorithm is stream-based, i.e. it processes the haystack character by character, so this is not a problem.

The test cases come one after another, each occupying three lines, with no additional space or line breaks in between.


For each test case your program should output all positions of the needle's occurences within the haystack. If a match is found, the output should contain the position of the first character of the match. Characters in the haystack are numbered starting with zero.

For a given test case, the positions output should be sorted in ascending order, and each of these should be printed in a separate line. For two different test cases, the positions should be separated by an empty line.


Sample input:
Sample output:


Note the double empty line in the output, which means that no match was found for the second test case.

Warning: large Input/Output data, be careful with certain languages

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Martijn Muijsers: 2013-12-23 19:04:59

Yes! Awesome! Broke my record: 10 consecutive new problems AC without any 'orange'! :D

Edit: Nobody cares

Last edit: 2014-01-16 17:36:40
arbit: 2013-12-13 14:28:02

I am using KMP in C. but still getting TLE. Any suggestions? I am reading the second string char by char in a while loop. and termination condition is while(eof != scanf("%c",&ch)). Anything wrong?

harsh: 2013-11-06 13:09:50

chngd cin to scanf AC...!!

Anmol Agarwal: 2013-09-05 08:51:46

any suggestion on not reading the haystack at once

sobhan: 2013-07-26 22:22:53

i used rabin-karp algo and i got TLE :'(
now i got wrong answer :O just used scanf and printf
finally i got acc :D

Last edit: 2013-07-27 11:51:35
Aswin Murugesh: 2013-06-12 05:11:00

What is the terminating condition in python?

Dark Knight: 2013-05-22 09:47:19

More test Cases ....
getting WA
are there sapces in needla and haystack ????

v.nandhini: 2013-02-23 05:35:47

I am using Printf&Scanf

Surya kiran: 2012-12-26 15:11:30

do the strings contain only small letter alphabet??

mayank: 2012-12-15 14:23:37

Am using strstr() function, god knows why it is returning TLE, Isnt strstr() faster than KMP? I am accepting haystack at once

Added by:mima
Time limit:5s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)