https://leetcode.com/problems/range-sum-query-2d-immutable/class NumMatrix: def __init__(self, matrix: List[List[int]]): ROWS, COLS = len(matrix) , len(matrix[0]) self.sumMat = [[0] * (COLS + 1) for c in range(ROWS+1)] for r in range(ROWS): prefix = 0 for c in range(COLS): prefix += matrix[r][c] above = self.sumMat[r][c+..