docs: complete question 3

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diff --git a/src/03/03/README.md b/src/03/03/README.md
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@@ -2,4 +2,21 @@ Suppose you are given two sequences S1 and S2 of `n` elements, possibly
 containing duplicates, on which a total order relation is defined.
 
 1. Describe an efficient algorithm for determining if S1 and S2 contain the same set of elements.
+
+Since S1 and S2 has a total order relation defined this means
+that the data is sorted in both sequences.
+
+To tell if the S1 and S2 contain the same set of elements we can use two pointers
+to walk through each item in each sequence one step at a time to compare the values
+at each index to ensure they are a match. As soon as we detect a mismatch
+we know that the sequences do not contain the same set of elements. If we can
+iterate to the end of both sequences at the same time then we have a match.
+
 1. Analyze the running time of this method.
+
+The time complexity is dependent on the size of `n` elements and is
+therefore a linear time algorithm `O(n)`.
+
+The space complexity is constant, `O(1)`, because only two pointers
+are needed to walk through both sequences. The amount of space required
+to perform this algorithm does not change as the input size of `n` changes.