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Hi everyone.

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Let's do this question.

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Evaluate the value of an arithmetic expression in reverse Polish notation c example.

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So this is an example of reverse Polish notation.

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All right.

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So valid operators are plus minus into and division.

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Note that division between two integers integers should truncate towards zero.

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That means you have to round it down.

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It is guaranteed that the given RPN or reverse Polish notation expression is always valid.

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That means the expression would always evaluate to a result, and there will not be any division by

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zero operation, so we don't need to check that.

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So there can be these edge cases.

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And we don't need to be worried about that because it's guaranteed that the expression will be valid.

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All right.

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The input is an array of strings where each element is either a valid operator or an integer.

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So this is an example.

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So let's take a look at this example over here to understand this question in a better manner.

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Let's say the input given is this array over here.

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So you can see over here we have a string with value one, a string with value two and a string with

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the plus operator.

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Now this means we take this one over here which is this one.

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We take this two which is the second number.

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And then we apply this operator over here.

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And this expression if this is the input the output expected is equal to three.

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Now let's take a look at one more example to understand this better.

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Let's say the array given is one, two three plus and minus.

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Now in this case we first have to evaluate this over here two three and plus.

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So we can see that this is plus.

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So the two numbers before it we have two and three.

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So this actually this part over here is two.

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Plus three.

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So this simplifies to five.

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And then it's equal to one five and minus which is one minus five.

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That's how we get one minus five over here which is equal to minus four.

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All right.

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So we have understood the question.

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Now let's take a look at a few test cases.

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Let's say we already have taken care of these two test cases.

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So if it's one, two and plus, it means one plus two, that's equal to three, one, two, three plus

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and minus.

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So two three plus this over here simplifies to five.

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And then we get it should be one minus five right.

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So this is one and then five.

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So this is equivalent to one five and minus.

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And this simplifies to one minus five which is equal to minus four.

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And if the expression expression is four three and division.

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So this is equal to four divided by three right.

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And this is equal to 1.33 etc..

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And in the question it's mentioned that in the case of division this has to be truncated towards zero.

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So that means this has to be rounded down.

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So 1.33 becomes one.

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All right.

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So again let's take a look at a bigger bigger example.

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All right.

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So let's say this is the array which is given to us.

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Now let's try to simplify this.

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We see two then three then four.

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And then we have plus over here.

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So the previous two over here is three and four.

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So this over here simplifies to three plus four which is equal to seven.

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So we have two seven and then a minus.

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So this over here simplifies to two minus seven.

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Right.

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So two minus seven gives us minus five.

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So let me just remove this.

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And I'm just replacing this with minus five.

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And then we have minus five seven and into.

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So this is minus five into seven which is equal to -35.

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So if this array was the input then we would have to return -35.

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So we have got a good understanding of the question.

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So let's go ahead and think about how we can solve this question in the next video.