LeetCode 3070 | Count Submatrices ≤ k | Prefix Sum | Java | Medium скачать в хорошем качестве

LeetCode 3070 | Count Submatrices ≤ k | Prefix Sum | Java | Medium

Today's LeetCode Daily Problem: You are given a grid and an integer k. Goal Count the number of submatrices that start from the top-left corner and have a sum less than or equal to k. Core Idea We use the Prefix Sum technique to efficiently compute submatrix sums. Step 1 Convert the grid into a prefix sum matrix. Each cell stores the sum of all elements from (0,0) to (i,j). Step 2 Use the formula: sum(i, j) = grid[i][j] top left top-left overlap This gives the sum of the submatrix from (0,0) to (i,j). Step 3 For every cell: Check if prefix sum ≤ k If yes, increment count Step 4 Return the total count Why This Works Since all submatrices must start from the top-left corner, each prefix sum directly represents a valid submatrix sum. This avoids recomputation and keeps the solution efficient. Time Complexity O(m multiplied by n) Space Complexity O(1) (in-place modification of grid) Concepts Used Prefix Sum Matrix Traversal Problem Link https://leetcode.com/problems/count-s... Java Solution (GitHub) https://github.com/Amandf/LeetCode-So... Daily LeetCode consistency #leetcode #leetcodesolution #leetcodedailychallenge #java #dsa #prefixsum #matrix #coding #programming #problemsolving