Let's assume we have the strings: "windows" and "linux". Create a first array of chars that contains the characters of the first string sorted by ascii code. [d,i,n,o, s,w, w]. Let's name this array A Create a second array of chars that contains the characters of the second string sorted by ascii code. [i, l, n, u ,x]. Let's name this array B. The pseudo algorithm will be as follow: posA = 0 posB = 0 while(posA < A.length && posB < B.length) { if (A[posA] == B[posB]) { print "find common character = " + A[posA]; posA++; posB++; } else if (A[posA] < B[posB]) { posA++; } else { posB++; } }