Beats 91% fully explained
Intuition\nThe numSubmatrixSumTarget function calculates the number of submatrices within the given matrix that sum up to the target value.\n\n# Approach\nItera
# Intuition\nThe numSubmatrixSumTarget function calculates the number of submatrices within the given matrix that sum up to the target value.\n\n# Approach\nIterate through each row of the matrix (i):\nFor each row, initialize a prefix sum array (prefixSums) to store the cumulative sums of elements in that row.\nIterate through each subsequent row (j) starting from i:\nUpdate the prefixSums array to include the cumulative sums of elements in the current row (j).\nUse a hashmap (seen) to keep track of the cumulative sums encountered so far and their frequencies.\nInitialize currentSum to 0 to keep track of the cumulative sum of subarrays.\nIterate through each column (k) to calculate the cumulative sum (currentSum) of subarrays ending at column k.\nCheck if there exists a previous subarray with the required complement (currentSum - target). If so, increment the count by the frequency of that complement in seen.\nUpdate the hashmap seen with the current cumulative sum (currentSum).\nAfter processing all submatrices, return the count, which represents the number of submatrices with the target sum.\n\n\n# Complexity\n- Time complexity:\nO(m^2 * n)\n\n- Space complexity:\nO(n)\n\n# Code\n```\nfunction numSubmatrixSumTarget(matrix, target) {\n  const m = matrix.length;\n  const n = matrix[0].length;\n  let count = 0;\n\n  for (let i = 0; i < m; i++) {\n    const prefixSums = new Array(n).fill(0);\n    for (let j = i; j < m; j++) {\n      for (let k = 0; k < n; k++) {\n        prefixSums[k] += matrix[j][k];\n      }\n      const seen = new Map();\n      seen.set(0, 1); \n      let currentSum = 0;\n      for (let k = 0; k < n; k++) {\n        currentSum += prefixSums[k];\n        count += seen.get(currentSum - target) || 0; \n        seen.set(currentSum, (seen.get(currentSum) || 0) + 1);\n      }\n    }\n  }\n\n  return count;\n}\n\n```
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