Substring algorithm

Question

Can someone explain to me how to solve the substring problem iteratively?

The problem: given two strings S=S₁S₂S

Answer 1

A naive algorithm would be to test at each position 0 < i ≤ n-m of S if S_i+1S_i+2…S_i+m=T₁T₂…T_m. For n=7 and m=5:

i=0:  S1S2S3S4S5S6S7
      | | | | |
      T1T2T3T4T5

i=1:  S1S2S3S4S5S6S7
        | | | | |
        T1T2T3T4T5

i=2:  S1S2S3S4S5S6S7
          | | | | |
          T1T2T3T4T5

The algorithm in pseudo-code:

// we just need to test if n ≤ m 
IF n > m:
    // for each offset on that T can start to be substring of S
    FOR i FROM 0 TO n-m:
        // compare every character of T with the corresponding character in S plus the offset
        FOR j FROM 1 TO m:
            // if characters are equal
            IF S[i+j] == T[j]:
                // if we’re at the end of T, T is a substring of S
                IF j == m:
                    RETURN true;
                ENDIF;
            ELSE:
                BREAK;
            ENDIF;
        ENDFOR;
    ENDFOR;
ENDIF;
RETURN false;