304.二维区域和检索-矩阵不可变.cpp

/*
 * @lc app=leetcode.cn id=304 lang=cpp
 *
 * [304] 二维区域和检索 - 矩阵不可变
 */

// @lc code=start
#include<iostream>
#include<vector>

using namespace std;

class NumMatrix {
public:
    vector<vector<int>> dp;
    NumMatrix(vector<vector<int>>& matrix) {
        int m = matrix.size();
        if(m==0)return;
        int n = matrix[0].size();
        dp = vector<vector<int>>(m+1, vector<int>(n+1, 0));
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                dp[i+1][j+1] = dp[i+1][j]+ dp[i][j+1] + matrix[i][j] - dp[i][j];
            }
        }
    }
    
    int sumRegion(int row1, int col1, int row2, int col2) {
        return dp[row2+1][col2+1] - dp[row1][col2+1] - dp[row2+1][col1] + dp[row1][col1];
    }
};

/**
 * Your NumMatrix object will be instantiated and called as such:
 * NumMatrix* obj = new NumMatrix(matrix);
 * int param_1 = obj->sumRegion(row1,col1,row2,col2);
 */
// @lc code=end