To minimize boats, we should pair the heaviest person with the lightest person if possible. If the sum exceeds the limit, the heaviest person must go in a boat alone.

1. Sort people.
2. l = 0, r = len(people) - 1, boats = 0.
3. While l <= r:
   • If people[l] + people[r] <= limit:
     • l += 1 (pair found).
   • r -= 1 (heavy person always takes a boat).
   • boats += 1.
4. Return boats.

• Time Complexity: O(N log N).
• Space Complexity: O(1).

def num_rescue_boats(people, limit):
    people.sort()
    l, r = 0, len(people) - 1
    boats = 0
    
    while l <= r:
        if people[l] + people[r] <= limit:
            l += 1
        r -= 1
        boats += 1
        
    return boats