source: https://leetcode.com/problems/boats-to-save-people/description/
Boats to Save People
You are given an array people where people[i] is the weight of the ith person, and an infinite number of boats where each boat can carry a maximum weight of limit. Each boat carries at most two people at the same time, provided the sum of the weight of those people is at most limit.
Return the minimum number of boats to carry every given person.
Example 1:
Input: people = [1,2], limit = 3
Output: 1
Explanation: 1 boat (1, 2)
Example 2:
Input: people = [3,2,2,1], limit = 3
Output: 3
Explanation: 3 boats (1, 2), (2) and (3)
Example 3:
Input: people = [3,5,3,4], limit = 5
Output: 4
Explanation: 4 boats (3), (3), (4), (5)
Constraints:
- 1 <= people.length <= 5 * 104
- 1 <= people[i] <= limit <= 3 * 104
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class Solution { public int numRescueBoats(int[] people, int limit) { Arrays.sort(people); int lo = 0; int hi = people.length-1; int count = 0; while(lo<hi){ int weight = people[lo] + people[hi]; if(weight <= limit){ count++; lo++; hi--; } else { count++; hi--; } } //to handle a case where lo==hi return lo==hi?count+1:count; } } |
Let’s say n is the number of people
Time Complexity
O(nlogn + nlogn), sort the people array + binary search (in the worst case weight is always greater than the limit)
Space Complexity
O(1)