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Hi everyone, I hope you have given it a try to code the brute force solution which we discussed in

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the previous video.

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Now in this video, let's do it together.

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Now for this we create a function and let's call it find non repeating character.

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And this function takes in a string as input.

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Now what we are going to do is let me just parallelly show that over here.

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Now let's say that the input string is a, b, c, d.

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B a d.

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Let's say this is the input string for example.

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Now what we're going to do is we will take one character, let's say over here that's a and compare

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it with all the other characters to see whether it's repeating.

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Right.

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So there we need a variable to keep track whether the particular character which we are trying to see,

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whether it's repeating or not, is actually repeating or not.

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So we need a variable for that.

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So let me declare a variable.

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Repeat for that over here.

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Now to traverse the given string we will use a for loop.

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So let's say for let I is equal to zero I less than string dot length.

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I plus plus.

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So we will traverse the array with this for loop.

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With this the traverse the string with this for loop.

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All right.

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Now when we enter this for loop let's set repeat to be equal to false.

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So we assume that the character is non-repeating.

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Now what we are going to do is we are going to traverse the string again with another for loop right.

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So let's say for let j equal to zero j less than string dot length.

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And J plus.

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Plus.

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Now, when we do this, we are going to compare the character at the ith and jth index of the given

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string.

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That's what you're going to do.

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You're going to check if string at the ith index is equal to string at the jth index.

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Now if this is true, it means that the string at the ith index is repeating.

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Right.

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For example, over here we are taking a and we are checking a with all the other characters over here.

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Now when we reach over here, we can see that yes, it's repeating right now.

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There's one more thing to be kept in mind over here.

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Notice that over here I can take values from zero to string dot length minus one.

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Similarly, j can take values from zero to string dot length minus one.

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So if I is equal to j, always the characters at those two indices will be the same.

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But that's not what we are trying to do over here.

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Right?

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When I have a of string of I as a, I need to check it with all the other indices, the characters at

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the other indices.

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So I need to add a condition over here that I should not be equal to j, so I not equal to j.

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Now if this is true, that is when I is not equal to j, but still the character at the ith index in

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the given string and the character at the jth index in the given string are equal.

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If this is true, it means that the character at the ith index is repeating, so we will set.

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Repeat is equal to true in this case.

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So in this way we will traverse the array using j.

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Now at the end of this for loop.

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So when we come out of this for loop we will check whether repeat is true or false.

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So if repeat at this point is equal to false.

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It means that we checked string I with all the other characters in the given string by changing the

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value of J, right.

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So we kept checking this and we got the value of repeat as false.

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That is, it never went inside over here.

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So if repeat is false it means that.

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The character at the ith index is non-repeating.

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So all we need to do is we just need to return the index, which is I.

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So that means the character at the ith index is non-repeating.

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Now if we go through all the elements of the given string, let's say the input was a, b, c, d,

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let's say the input was a a b b c, c.

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So we take all the values of I so zero one, two, three, four five.

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We keep doing that but we were never able to return anything.

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So always return.

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Repeat was true.

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So it never returned anything.

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So we come out of this for loop.

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At this point we just need to return null because we clarified from the interviewer that if we are not

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able to find a non-repeating character, we can just return null.

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So at this point we will return null and we have our solution.

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Now let's test our solution.

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Let's say string.

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Let's say a is equal to this string over here a a b b c c.

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Now in this case we should get null as output.

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So let's try to see whether that's working.

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So console dot log find non-repeating character.

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And we are passing a over here.

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Now let's run this and see what we are getting.

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So when we run this, we are having an error over here.

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Okay.

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So we did not write an equal to over here.

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Okay.

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So repeat is equal to true in this case.

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So let's run it again.

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All right.

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So when we run it, we can see that we are getting null because all of these characters are repeating,

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what if I add D over here and again run it.

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So in this case I'm getting six over here 120123456.

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That's the index of D.

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So it's working right now let's try a few combinations.

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What if it's a a and uh a b.

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So in this case we should get zero one.

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Which is the index where capital A is there.

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So that's the correct answer.

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We are getting the correct answer over here.

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Now what if we have an empty string.

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In this case we are getting null as output which is correct.

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And what if we have a string?

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Where we have a number, let's say we have one, two a, one, two, three, four, and then we have

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one, two and a.

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So it should give us the index of three which is 1230123.

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So the answer in this case should be three.

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Let's see.

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And we are getting the answer as three.

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So yes our algorithm is working.

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Now let's take a look at this code.

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Let's take a test case and walk through this code again.