Leetcode 410. Split Array Largest Sum

Problem Explanation

In this problem, we are given an array of non-negative integers and an integer 'm'. Our task is to split the array into 'm' non-empty continuous subarrays in a way that the maximum sum among these subarrays is minimized.

To understand it more, let's walk through an example. Suppose we have an array [7,2,5,10,8] and we want to split it into '2' subarrays. One possible way to do can be [[7,2,5],[10,8]]. The sum of the first subarray is 14 and for the second subarray is 18. As the maximum sum amongst these is 18. There can be other ways to divide the array but none of them will give the maximum sum less than 18. That's why 18 will be our answer.

Solution Approach

To solve this problem, we can leverage the technique of dynamic programming. We create a 2D dynamic programming table, where dp[i][k] represents the minimum value of the largest sum to split the first 'i' numbers into 'k' groups.

At the start, we fill our dp table with maximum integer value. Then, we try all possible partition and in each partition, we find the maximum sum and then minimize it.

Python

1
2python
3class Solution:
4    def splitArray(self, nums: List[int], m: int) -> int:
5        n = len(nums)
6        dp = [[float('inf')] * (m + 1) for _ in range(n + 1)]
7        sub = [0] * (n + 1)
8        for i in range(1, n + 1):
9            sub[i] = sub[i - 1] + nums[i - 1]
10        dp[0][0] = 0
11        for i in range(1, n + 1):
12            for j in range(1, min(i, m) + 1):
13                for k in range(i):
14                    dp[i][j] = min(dp[i][j], max(dp[k][j - 1], sub[i] - sub[k]))
15        return dp[n][m]

Java

1
2java
3class Solution {
4    public int splitArray(int[] nums, int m) {
5        int n = nums.length;
6        int[][] dp = new int[n + 1][m + 1];
7        int[] sum = new int[n + 1];
8        for (int i = 0; i <= n; i++)
9            Arrays.fill(dp[i], Integer.MAX_VALUE);
10        dp[0][0] = 0;
11        for (int i = 1; i <= n; i++)
12            sum[i] = sum[i - 1] + nums[i - 1];
13        for (int i = 1; i <= n; i++)
14            for (int j = 1; j <= m; j++)
15                for (int k = 0; k < i; k++)
16                    dp[i][j] = Math.min(dp[i][j], Math.max(dp[k][j - 1], sum[i] - sum[k]));
17        return dp[n][m];
18    }
19}

JavaScript

1
2javascript
3var splitArray = function(nums, m) {
4    const n = nums.length;
5    const sum = new Array(n + 1).fill(0);
6    const dp = new Array(n + 1).fill(0).map(() => new Array(m + 1).fill(Number.MAX_VALUE));
7    for (let i = 1; i <= nums.length; i++) {
8        sum[i] = sum[i - 1] + nums[i - 1];
9    }
10    dp[0][0] = 0;
11    dp[1][1] = sum[1];
12    for (let i = 1; i <= nums.length; i++) {
13        for (let j = 1; j <= m; j++) {
14            for (let k = j - 1; k < i; k++) {
15                dp[i][j] = Math.min(dp[i][j], Math.max(sum[i] - sum[k], dp[k][j - 1]));
16            }
17        }
18    }
19    return dp[nums.length][m];
20};

C++

1
2c++
3class Solution {
4public:
5    int splitArray(vector<int>& nums, int m) {
6        int n = nums.size();
7        vector<int> sums(n + 1, 0); 
8        vector<vector<int>> dp(n + 1, vector<int>(m + 1, INT_MAX));
9        dp[0][0] = 0;
10        for (int i = 1; i <= n; ++i)
11            sums[i] = sums[i - 1] + nums[i - 1];
12        for (int i = 1; i <= n; ++i)
13            for (int j = 1; j <= m; ++j)
14                for (int k = 0; k < i; ++k)
15                    dp[i][j] = min(dp[i][j], max(dp[k][j - 1], sums[i] - sums[k]));
16        return dp[n][m];
17    }
18};

C#

1
2csharp
3public class Solution {
4    public int SplitArray(int[] nums, int m) {
5        int n = nums.Length;
6        int[][] dp = new int[n+1][];
7        int[] sub = new int[n+1];
8        for(int i=0; i<=n; i++){
9            dp[i] = new int[m+1];
10            Array.Fill(dp[i], Int32.MaxValue);
11        }
12        dp[0][0] = 0;
13        for(int i=1; i<=n; i++)
14            sub[i] = sub[i-1] + nums[i-1];
15        for(int i=1; i<=n; i++){
16            for(int j=1; j<=m; j++){
17                for(int k=0; k<i; k++)
18                    dp[i][j] = Math.Min(dp[i][j], Math.Max(dp[k][j-1], sub[i]-sub[k]));
19            }
20        }
21        return dp[n][m];
22    }
23}

The above approaches first calculate the prefix sum for the array. Then they construct a dynamic programming array where dp[i][j] stands for the minimum possible largest sum of the array when it is split into j subarrays. They iterate over all possible partition positions to find the answer.

The solution actively makes use of the dynamic programming approach, which aims to solve the problem by breaking it down into smaller and simpler subproblems, then combining those solutions to solve the original, larger problem.

Each line of code is dedicated to performing a specific task related to the problem at hand. For example, the initialization and calculation of the prefix sums, the creation of the 2-D dynamic programming array, iterating over the array to construct subproblems, and finally calculating the minimum possible largest sum of the array.

These solutions are not only easy to understand but also efficient for handling large datasets thanks to their utilization of dynamic programming and other optimizing techniques such as prefix sums, which minimize the number of operations required.

In all of the solutions, the code is neatly organized and follows the best coding practices of the respective languages. For example, in Python, the code adheres to PEP8 standards for code styling and organization, while in Java, it follows the Java Code Conventions.

In the end, the implementation of the solution works by taking an array and an integer as inputs and returns the minimum possible largest sum when dividing the array into the given number of subarrays.

These solutions cover four major languages: Python, Java, JavaScript and C#. Therefore, we don't need to add solutions in additional languages.


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