Leetcode 3594. Minimum Time to Transport All Individuals

• Leetcode 3594. Minimum Time to Transport All Individuals
  • 1. 解题思路
  • 2. 代码实现

• 题目链接：3594. Minimum Time to Transport All Individuals

1. 解题思路

这一题思路上算是一个宽度优先遍历吧，我们就是不断地考察当前情况下的用时最少运输方法，以及其后续可能的运输方法，直至第一次将所有人都送到对岸。

不过具体做法上容易踩坑，就是没考虑好情况的话就容易出错，反正我这次错了好多次，最后倒是改对了，但是思路上其实和一开始做的也没啥变化，就是写法上不断优化，这里就不展开了，对着代码看看反正还挺好懂的。

2. 代码实现

给出python代码实现如下：

class Solution:
    def minTime(self, n: int, k: int, m: int, time: List[int], mul: List[float]) -> float:
        if k == 1:
            return -1 if n >= 2 else time[0] * mul[0]

        q = [(0, 0, 0, 0)] # (time, status, stage, edge)
        seen = set()
        while q:
            t, status, stage, edge = heapq.heappop(q)
            if status == 2**n-1:
                return t
            elif (status, stage, edge) in seen:
                continue
            seen.add((status, stage, edge))
            if edge == 0:
                candidates = [i for i in range(n) if status & (1<<i) == 0]
                for kn in range(min(k, len(candidates)), 0, -1):
                    for group in combinations(candidates, kn):
                        t_go = max([time[i] for i in group]) * mul[stage]
                        updated_status = 0
                        for i in group:
                            updated_status |= (1<<i)
                        new_status = status | updated_status
                        new_stage = (stage + int(t_go)) % m
                        if (new_status, new_stage, 1) not in seen:
                            heapq.heappush(q, (t+t_go, new_status, new_stage, 1))
            else:
                reached = [i for i in range(n) if status & (1<<i) != 0]
                for i in reached:
                    t_back = time[i] * mul[stage]
                    new_status = status - (1<<i)
                    new_stage = (stage + int(t_back)) % m
                    if (new_status, new_stage, 0) not in seen:
                            heapq.heappush(q, (t+t_back, new_status, new_stage, 0))
        return -1

提交代码评测得到：耗时8815ms，占用内存135.42MB。