rangeSumQuery2D-Immutable.py

#! /usr/bin/env python3
# -*- coding: utf-8 -*-

# Source: https://leetcode.com/problems/range-sum-query-2d-immutable/
# Author: Miao Zhang
# Date:   2021-02-01

class NumMatrix:

    def __init__(self, matrix: List[List[int]]):
        if not matrix: 
            self.dp = [[0]]
            return 
        m = len(matrix)
        n = len(matrix[0])
        self.dp = [[0 for _ in range(n + 1)] for _ in range(m + 1)]
        for i in range(1, m + 1):
            for j in range(1, n + 1):
                self.dp[i][j] = self.dp[i - 1][j] + self.dp[i][j - 1] - self.dp[i - 1][j - 1] + matrix[i - 1][j - 1]
        
    def sumRegion(self, row1: int, col1: int, row2: int, col2: int) -> int:
        return self.dp[row2 + 1][col2 + 1] - self.dp[row2 + 1][col1] - self.dp[row1][col2 + 1] + self.dp[row1][col1]


# Your NumMatrix object will be instantiated and called as such:
# obj = NumMatrix(matrix)
# param_1 = obj.sumRegion(row1,col1,row2,col2)