LeetCode #1594 — MEDIUM

Maximum Non Negative Product in a Matrix

Move from brute-force thinking to an efficient approach using array strategy.

The Problem

Problem Statement

You are given a m x n matrix grid. Initially, you are located at the top-left corner (0, 0), and in each step, you can only move right or down in the matrix.

Among all possible paths starting from the top-left corner (0, 0) and ending in the bottom-right corner (m - 1, n - 1), find the path with the maximum non-negative product. The product of a path is the product of all integers in the grid cells visited along the path.

Return the maximum non-negative product modulo 10⁹ + 7. If the maximum product is negative, return -1.

Notice that the modulo is performed after getting the maximum product.

Example 1:

Input: grid = [[-1,-2,-3],[-2,-3,-3],[-3,-3,-2]]
Output: -1
Explanation: It is not possible to get non-negative product in the path from (0, 0) to (2, 2), so return -1.

Example 2:

Input: grid = [[1,-2,1],[1,-2,1],[3,-4,1]]
Output: 8
Explanation: Maximum non-negative product is shown (1 * 1 * -2 * -4 * 1 = 8).

Example 3:

Input: grid = [[1,3],[0,-4]]
Output: 0
Explanation: Maximum non-negative product is shown (1 * 0 * -4 = 0).

Constraints:

m == grid.length
n == grid[i].length
1 <= m, n <= 15
-4 <= grid[i][j] <= 4

Step 01

Brute Force Baseline

Problem summary: You are given a m x n matrix grid. Initially, you are located at the top-left corner (0, 0), and in each step, you can only move right or down in the matrix. Among all possible paths starting from the top-left corner (0, 0) and ending in the bottom-right corner (m - 1, n - 1), find the path with the maximum non-negative product. The product of a path is the product of all integers in the grid cells visited along the path. Return the maximum non-negative product modulo 109 + 7. If the maximum product is negative, return -1. Notice that the modulo is performed after getting the maximum product.

Baseline thinking

Start with the most direct exhaustive search. That gives a correctness anchor before optimizing.

Pattern signal: Array · Dynamic Programming

Example 1

[[-1,-2,-3],[-2,-3,-3],[-3,-3,-2]]

Example 2

[[1,-2,1],[1,-2,1],[3,-4,1]]

Example 3

[[1,3],[0,-4]]

Step 02

Core Insight

What unlocks the optimal approach

Use Dynamic programming. Keep the highest value and lowest value you can achieve up to a point.

Interview move: turn each hint into an invariant you can check after every iteration/recursion step.

Step 03

Algorithm Walkthrough

Iteration Checklist

Define state (indices, window, stack, map, DP cell, or recursion frame).
Apply one transition step and update the invariant.
Record answer candidate when condition is met.
Continue until all input is consumed.

Use the first example testcase as your mental trace to verify each transition.

Step 04

Edge Cases

Minimum Input

Single element / shortest valid input

Validate boundary behavior before entering the main loop or recursion.

Duplicates & Repeats

Repeated values / repeated states

Decide whether duplicates should be merged, skipped, or counted explicitly.

Extreme Constraints

Upper-end input sizes

Re-check complexity target against constraints to avoid time-limit issues.

Invalid / Corner Shape

Empty collections, zeros, or disconnected structures

Handle special-case structure before the core algorithm path.

Step 05

Full Annotated Code

Source-backed implementations are provided below for direct study and interview prep.

// Accepted solution for LeetCode #1594: Maximum Non Negative Product in a Matrix
class Solution {
    private static final int MOD = (int) 1e9 + 7;

    public int maxProductPath(int[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        long[][][] dp = new long[m][n][2];
        dp[0][0][0] = grid[0][0];
        dp[0][0][1] = grid[0][0];
        for (int i = 1; i < m; ++i) {
            dp[i][0][0] = dp[i - 1][0][0] * grid[i][0];
            dp[i][0][1] = dp[i - 1][0][1] * grid[i][0];
        }
        for (int j = 1; j < n; ++j) {
            dp[0][j][0] = dp[0][j - 1][0] * grid[0][j];
            dp[0][j][1] = dp[0][j - 1][1] * grid[0][j];
        }
        for (int i = 1; i < m; ++i) {
            for (int j = 1; j < n; ++j) {
                int v = grid[i][j];
                if (v >= 0) {
                    dp[i][j][0] = Math.min(dp[i - 1][j][0], dp[i][j - 1][0]) * v;
                    dp[i][j][1] = Math.max(dp[i - 1][j][1], dp[i][j - 1][1]) * v;
                } else {
                    dp[i][j][0] = Math.max(dp[i - 1][j][1], dp[i][j - 1][1]) * v;
                    dp[i][j][1] = Math.min(dp[i - 1][j][0], dp[i][j - 1][0]) * v;
                }
            }
        }
        long ans = dp[m - 1][n - 1][1];
        return ans < 0 ? -1 : (int) (ans % MOD);
    }
}

// Accepted solution for LeetCode #1594: Maximum Non Negative Product in a Matrix
func maxProductPath(grid [][]int) int {
	m, n := len(grid), len(grid[0])
	dp := make([][][]int, m)
	for i := range dp {
		dp[i] = make([][]int, n)
		for j := range dp[i] {
			dp[i][j] = make([]int, 2)
		}
	}
	dp[0][0] = []int{grid[0][0], grid[0][0]}
	for i := 1; i < m; i++ {
		dp[i][0][0] = dp[i-1][0][0] * grid[i][0]
		dp[i][0][1] = dp[i-1][0][1] * grid[i][0]
	}
	for j := 1; j < n; j++ {
		dp[0][j][0] = dp[0][j-1][0] * grid[0][j]
		dp[0][j][1] = dp[0][j-1][1] * grid[0][j]
	}
	for i := 1; i < m; i++ {
		for j := 1; j < n; j++ {
			v := grid[i][j]
			if v >= 0 {
				dp[i][j][0] = min(dp[i-1][j][0], dp[i][j-1][0]) * v
				dp[i][j][1] = max(dp[i-1][j][1], dp[i][j-1][1]) * v
			} else {
				dp[i][j][0] = max(dp[i-1][j][1], dp[i][j-1][1]) * v
				dp[i][j][1] = min(dp[i-1][j][0], dp[i][j-1][0]) * v
			}
		}
	}
	ans := dp[m-1][n-1][1]
	if ans < 0 {
		return -1
	}
	var mod int = 1e9 + 7
	return ans % mod
}

# Accepted solution for LeetCode #1594: Maximum Non Negative Product in a Matrix
class Solution:
    def maxProductPath(self, grid: List[List[int]]) -> int:
        m, n = len(grid), len(grid[0])
        mod = 10**9 + 7
        dp = [[[grid[0][0]] * 2 for _ in range(n)] for _ in range(m)]
        for i in range(1, m):
            dp[i][0] = [dp[i - 1][0][0] * grid[i][0]] * 2
        for j in range(1, n):
            dp[0][j] = [dp[0][j - 1][0] * grid[0][j]] * 2
        for i in range(1, m):
            for j in range(1, n):
                v = grid[i][j]
                if v >= 0:
                    dp[i][j][0] = min(dp[i - 1][j][0], dp[i][j - 1][0]) * v
                    dp[i][j][1] = max(dp[i - 1][j][1], dp[i][j - 1][1]) * v
                else:
                    dp[i][j][0] = max(dp[i - 1][j][1], dp[i][j - 1][1]) * v
                    dp[i][j][1] = min(dp[i - 1][j][0], dp[i][j - 1][0]) * v
        ans = dp[-1][-1][1]
        return -1 if ans < 0 else ans % mod

// Accepted solution for LeetCode #1594: Maximum Non Negative Product in a Matrix
struct Solution;

const MOD: i64 = 1_000_000_007;

impl Solution {
    fn max_product_path(grid: Vec<Vec<i32>>) -> i32 {
        let n = grid.len();
        let m = grid[0].len();
        let mut max = vec![vec![0; m]; n];
        let mut min = vec![vec![0; m]; n];
        max[0][0] = grid[0][0] as i64;
        min[0][0] = grid[0][0] as i64;
        for i in 1..n {
            max[i][0] = max[i - 1][0] * grid[i][0] as i64;
            min[i][0] = min[i - 1][0] * grid[i][0] as i64;
        }
        for j in 1..m {
            max[0][j] = max[0][j - 1] * grid[0][j] as i64;
            min[0][j] = min[0][j - 1] * grid[0][j] as i64;
        }
        for i in 1..n {
            for j in 1..m {
                if grid[i][j] < 0 {
                    max[i][j] = grid[i][j] as i64 * min[i][j - 1].min(min[i - 1][j]);
                    min[i][j] = grid[i][j] as i64 * max[i][j - 1].max(max[i - 1][j]);
                } else {
                    max[i][j] = grid[i][j] as i64 * max[i][j - 1].max(max[i - 1][j]);
                    min[i][j] = grid[i][j] as i64 * min[i][j - 1].min(min[i - 1][j]);
                }
            }
        }

        if max[n - 1][m - 1] < 0 {
            -1
        } else {
            (max[n - 1][m - 1] % MOD) as i32
        }
    }
}

#[test]
fn test() {
    let grid = vec_vec_i32![[-1, -2, -3], [-2, -3, -3], [-3, -3, -2]];
    let res = -1;
    assert_eq!(Solution::max_product_path(grid), res);
    let grid = vec_vec_i32![[1, -2, 1], [1, -2, 1], [3, -4, 1]];
    let res = 8;
    assert_eq!(Solution::max_product_path(grid), res);
    let grid = vec_vec_i32![[1, 3], [0, -4]];
    let res = 0;
    assert_eq!(Solution::max_product_path(grid), res);
    let grid = vec_vec_i32![[1, 4, 4, 0], [-2, 0, 0, 1], [1, -1, 1, 1]];
    let res = 2;
    assert_eq!(Solution::max_product_path(grid), res);
}

// Accepted solution for LeetCode #1594: Maximum Non Negative Product in a Matrix
// Auto-generated TypeScript example from java.
function exampleSolution(): void {
}
// Reference (java):
// // Accepted solution for LeetCode #1594: Maximum Non Negative Product in a Matrix
// class Solution {
//     private static final int MOD = (int) 1e9 + 7;
// 
//     public int maxProductPath(int[][] grid) {
//         int m = grid.length;
//         int n = grid[0].length;
//         long[][][] dp = new long[m][n][2];
//         dp[0][0][0] = grid[0][0];
//         dp[0][0][1] = grid[0][0];
//         for (int i = 1; i < m; ++i) {
//             dp[i][0][0] = dp[i - 1][0][0] * grid[i][0];
//             dp[i][0][1] = dp[i - 1][0][1] * grid[i][0];
//         }
//         for (int j = 1; j < n; ++j) {
//             dp[0][j][0] = dp[0][j - 1][0] * grid[0][j];
//             dp[0][j][1] = dp[0][j - 1][1] * grid[0][j];
//         }
//         for (int i = 1; i < m; ++i) {
//             for (int j = 1; j < n; ++j) {
//                 int v = grid[i][j];
//                 if (v >= 0) {
//                     dp[i][j][0] = Math.min(dp[i - 1][j][0], dp[i][j - 1][0]) * v;
//                     dp[i][j][1] = Math.max(dp[i - 1][j][1], dp[i][j - 1][1]) * v;
//                 } else {
//                     dp[i][j][0] = Math.max(dp[i - 1][j][1], dp[i][j - 1][1]) * v;
//                     dp[i][j][1] = Math.min(dp[i - 1][j][0], dp[i][j - 1][0]) * v;
//                 }
//             }
//         }
//         long ans = dp[m - 1][n - 1][1];
//         return ans < 0 ? -1 : (int) (ans % MOD);
//     }
// }

Step 06

Interactive Study Demo

Use this to step through a reusable interview workflow for this problem.

Custom checkpoints (one per line)

Press Step or Run All to begin.

Step 07

Complexity Analysis

Time

O(n × m)

Space

O(n × m)

Approach Breakdown

RECURSIVE

O(2ⁿ) time

O(n) space

Pure recursion explores every possible choice at each step. With two choices per state (take or skip), the decision tree has 2ⁿ leaves. The recursion stack uses O(n) space. Many subproblems are recomputed exponentially many times.

DYNAMIC PROGRAMMING

O(n × m) time

O(n × m) space

Each cell in the DP table is computed exactly once from previously solved subproblems. The table dimensions determine both time and space. Look for the state variables — each unique combination of state values is one cell. Often a rolling array can reduce space by one dimension.

Shortcut: Count your DP state dimensions → that’s your time. Can you drop one? That’s your space optimization.

Coach Notes

Common Mistakes

Review these before coding to avoid predictable interview regressions.

Off-by-one on range boundaries

Wrong move: Loop endpoints miss first/last candidate.

Usually fails on: Fails on minimal arrays and exact-boundary answers.

Fix: Re-derive loops from inclusive/exclusive ranges before coding.

State misses one required dimension

Wrong move: An incomplete state merges distinct subproblems and caches incorrect answers.

Usually fails on: Correctness breaks on cases that differ only in hidden state.

Fix: Define state so each unique subproblem maps to one DP cell.