881. Boats to Save People

Medium

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

解題

Runtime: 83 ms, faster than 100%

Memory Usage: 7.5 MB, less than 55.32%

func numRescueBoats(people []int, limit int) int {
    sort.Ints(people)
    ans := 0

    right, left := len(people) - 1, 0
    weight := 0 // 重量
    count := 0 // 船上人數
    for right >= left {
        // 重量剛好到達上限 / 不能再上船了 / 人數滿了 -> 換一艘船
        if weight == limit || weight + people[left] > limit || count == 2{
            ans++
            weight = 0
            count = 0
        } 

        if weight + people[right] <= limit {
            weight += people[right]
            count++
            right--
            continue
        } else {
            if weight + people[left] <= limit {
                weight += people[left]
                count++
                left++
            }
        }
    }

    return ans + 1 // 加上最後一艘船
}