String search in O(n + m)

Fri, 08 Jan 2010 00:00:00 +0000

Searching a string inside another string is a very easy task. Given a string A and a string B, start a loop over A from left to right and, for every letter, start an internal loop to see if there is a match with the letters of B.

A ball of string

Pseudo code would look something like this:

function NaiveSearch(string s[1..n], string sub[1..m])
   for i from 1 to n-m+1
      for j from 1 to m
         if s[i+j-1] ≠ sub[j]
            jump to next iteration of outer loop
      return i
   return not found

Time Complexity? O(n * m), where n is the size of A and m is the size of B.

Matching on Zio Ivan

String search in O(n + m)