AlgoDaily - Detect Substring in String

So given string geography and substring graph, we'd step it through like this:

g matches g, so j = 1
e does not match r, so j = 0
o does not match g, so j = 0
g does match g, so j = 1
r does match r, so j = 2
a does match a, so j = 3 and so on...

At the same time, we also need to keep track of the actual index that the match starts. The j index will help us get the matching, but we need a idxOfStart variable for just the start.

Putting it all together:

xxxxxxxxxx
 
let idxOfStart = 0;
let j = 0;
let str = 'digginn';
let subStr = 'inn';
​
for (i = 0; i < str.length; i++) {
  // if match, compare next character of subStr with next of string
  if (str[i] == subStr[j]) {
    j++;
  } else {
    j = 0;
  }
​
  // keep track of where match starts and ends
  if (j == 0) {
    idxOfStart = i;
  } else if (j == subStr.length) {
    console.log(idxOfStart);
    // we know this is the start of match
  }
}

OUTPUT

Results will appear here.