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Find Minimum Time to Finish All Jobs

You are given an integer array jobs, where jobs[i] is the amount of time it takes to complete the ith job.

There are k workers that you can assign jobs to. Each job should be assigned to exactly one worker. The working time of a worker is the sum of the time it takes to complete all jobs assigned to them. Your goal is to devise an optimal assignment such that the maximum working time of any worker is minimized.

Return the minimum possible maximum working time of any assignment.

 

Example 1:

Input: jobs = [3,2,3], k = 3
Output: 3
Explanation: By assigning each person one job, the maximum time is 3.

Example 2:

Input: jobs = [1,2,4,7,8], k = 2
Output: 11
Explanation: Assign the jobs the following way:
Worker 1: 1, 2, 8 (working time = 1 + 2 + 8 = 11)
Worker 2: 4, 7 (working time = 4 + 7 = 11)
The maximum working time is 11.

 

Constraints:

  • 1 <= k <= jobs.length <= 12
  • 1 <= jobs[i] <= 107

Solution Explanation:

This problem asks to find the minimum possible maximum working time of any worker when assigning jobs to k workers. The solution uses a backtracking approach with optimization to efficiently explore the assignment possibilities.

Approach:

  1. Sort Jobs: The jobs are sorted in descending order. This is a crucial optimization. Starting with the largest jobs first helps to quickly prune the search space. If a partial assignment already exceeds the current minimum maximum working time, there's no need to continue exploring that branch.

  2. Backtracking (DFS): A depth-first search (DFS) recursively explores all possible job assignments. dfs(i) represents the function that assigns jobs starting from index i.

  3. State: The state is maintained using an array cnt of size k. cnt[j] stores the total time worker j has spent on jobs assigned to them.

  4. Pruning: The condition if cnt[j] + jobs[i] >= ans is a vital pruning step. If assigning job i to worker j would result in a total time for that worker exceeding the current minimum maximum working time (ans), that assignment is immediately discarded. This significantly reduces the number of explored possibilities.

  5. Base Case: When all jobs have been assigned (i == len(jobs)), the maximum working time among all workers is calculated, and ans (the minimum maximum working time) is updated if a better assignment is found.

  6. Exploration: The algorithm iterates through each worker (j) for each job (i) and explores the possibility of assigning the current job to that worker. After the recursive call returns, the assignment is undone (cnt[j] -= jobs[i]) to backtrack and explore other possibilities. The if cnt[j] == 0: break condition further optimizes: if a worker has no jobs assigned, we don't need to consider it for subsequent job assignments as we are guaranteed to find a better assignment that assigns this job to a different worker.

Time Complexity Analysis:

The worst-case time complexity is O(kn), where n is the number of jobs and k is the number of workers. In the worst-case scenario, the algorithm might explore all possible assignments of jobs to workers. However, due to the significant pruning done by the cnt[j] + jobs[i] >= ans condition and the optimization to skip assignments that would exceed the current minimum (ans), the actual runtime is often much less than the theoretical worst case. The sorting step adds an extra O(n log n) time complexity, but this is dominated by the exponential complexity of the backtracking part for larger input sizes.

Space Complexity Analysis:

The space complexity is dominated by the recursion depth of the DFS, which is O(n) in the worst case. The cnt array uses O(k) space. Therefore, the overall space complexity is O(n + k).

Code in Different Languages:

The code implementations in Python, Java, C++, and Go demonstrate the backtracking approach with the optimization techniques described above. Each implementation closely follows the algorithm's steps. The Python solution uses inf (infinity) as an initial value for ans, while the other languages use a large integer value for the same purpose. The sorting step in all languages is done to optimize the pruning effect.