Check if a string is a substring of another

Run a loop from start to end and for every index in the given string check whether the sub-string can be formed from that index. This can be done by running a nested loop traversing the given string and in that loop running another loop checking for sub-strings starting from every index.

Follow the steps below to implement the idea:

• Run a for loop with counter i from 0 to N – M.
  • Run a for loop with counter j from 0 to M-1.
    • Compare j^th character of S₁ with (i+j)^th character of S_2.
    • If the loop terminates after matching all the characters, then return i, i.e. substring S₁ is found starting from i^th character of S₂
• Return -1 as no substring is found.

For example, consider there to be a string of length N and a substring of length M. Then run a nested loop, where the outer loop runs from 0 to (N-M) and the inner loop from 0 to M. For very index check if the sub-string traversed by the inner loop is the given sub-string or not.

Check if a string is a substring of another: https://www.geeksforgeeks.org/check-string-substring-another/