The input nums is supposed to be an array of unique integers ranging from 1 to nums. Length (inclusive). However, there is a mistake: one of the numbers in the array is duplicated, which means another number is missing. Find and return the sum of the duplicated number and the missing number. Example: in the array [4, 3, 3, 1],3 is present twice and 2 is missing, so 3+2= 5 should be returned.

The smokey mountains have over 2,100 miles of rushing mountain streams and rivers that flow through the park. in each mile lives a diverse community of native fish, amphibians, insects, and larvae, some of which are found only in the southern appalachians. park managers and scientific researchers test many factors such as fish populations, the watersheds and water tests to determine a) too many lizards are present b) the water quality of the stream c) rainwater is running into local streams d) if visitors to the park are overstaying their welcome