Leetcode 2295 replace elements in an array

Leetcode 2295 Replace elements in an array. The solution here is using dictionary/map data structure to track the corresponding value for each index. Essentially, as long as we know the value corresponding to each index after the replacements specified in `operations`. Notice that we use the `number:index` pair in the dictionary to make the `replacement` easy and fast. This provides another example that uses data structure to help solve a specific problem in this series.