Boats - Implementation

function numRescueBoats(people, limit)
 sort people ascending
 left := 0
 right := length of people - 1
 boats := 0
 while left <= right
 if people[left] + people[right] <= limit then
 left := left + 1
 right := right - 1
 boats := boats + 1
 return boats

Time: $O(n \log n)$. Space: $O(1)$ extra.