Shortest Common Super Sequence

Shortest common super-sequence is a sequence where each element of both of the given sequences is present. In other words, we can say that the given two strings, both are sub-sequence of Shortest Common Super-Sequence.

When there are no common characters in two strings, then we can simply concatenate them to get Super-sequence. But when they have some common characters, then firstly we have to find the longest string, then add extra characters of the other string.

Input and Output

Two strings. “ABCDEF” and “XYDEF”
The length of the shortest common super-sequence.
Here the super-sequence is “ABCDEFXY”. So the length is 8.


superSeq(str1, str2)

Input: Two strings str1 and str2.

Output: Find length of super sequence.

   m := length of str1
   n := length of str2
   define table named seqTab of size (m+1 x n+1)

   for i := 0 to m, do
      for j := 0 to n, do
         if i = 0, then
            seqTab[i, j] := j
         else if j = 0, then
            seqTab[i, j] := i
         else if str1[i-1] = str2[j-1], then
            seqTab[i, j] := 1 + seqTab[i-1, j-1]
            seqTab[i, j] := 1 + minimum of seqTab[i-1, j] and seqTab[i, j-1]
   return seqTab[m, n]


using namespace std;

int min(int a, int b) {
   return (a<b)?a:b;

int superSeq(string str1, string str2) {
   int m = str1.size();
   int n = str2.size();

   int supSeqTable[m+1][n+1];

   for (int i = 0; i <= m; i++) {
      for (int j = 0; j <= n; j++) {
         if (!i)
            supSeqTable[i][j] = j;              //shortest supersequence length is j
         else if (!j)
            supSeqTable[i][j] = i;                //shortest supersequence length is i
         else if (str1[i-1] == str2[j-1])
            supSeqTable[i][j] = 1 + supSeqTable[i-1][j-1];
            supSeqTable[i][j] = 1 + min(supSeqTable[i-1][j], supSeqTable[i][j-1]);
   return supSeqTable[m][n];

int main() {
   string first = "ABCDEF";
   string second = "XYDEF";
   cout << "Length of the shortest supersequence is " << superSeq(first, second);


Length of the shortest supersequence is 8