leetcode 304. Range Sum Query 2D - Immutable

You are given an integer array nums and you have to return a new counts array. The counts array has the property where counts[i] is the number of smaller elements to the right of nums[i].
Example:
Given nums = [5, 2, 6, 1]
To the right of 5 there are 2 smaller elements (2 and 1).
To the right of 2 there is only 1 smaller element (1).
To the right of 6 there is 1 smaller element (1).
To the right of 1 there is 0 smaller element.
Return the array [2, 1, 1, 0].
ニマ、これが積分図じゃないの?

// ConsoleApplication1.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include<vector>
#include<iostream>
using namespace std;
class NumMatrix {
private:
	vector<vector<int>>regionsum;
public:
	NumMatrix(vector<vector<int>> &matrix) {
		regionsum.resize(matrix.size()+1);
		if(matrix.empty())
			return;
		for(int i=0;i<matrix.size()+1;i++)
			regionsum[i].resize(matrix[0].size()+1);
		for(int i=1;i<matrix.size()+1;i++)
			for(int j=1;j<matrix[0].size()+1;j++)
			{
				regionsum[i][j]=regionsum[i-1][j]+regionsum[i][j-1]-regionsum[i-1][j-1]+matrix[i-1][j-1];
			}
	}

	int sumRegion(int row1, int col1, int row2, int col2) {
		if(regionsum.size()==1)
			return 0;
		if(regionsum[0].size()==1)
			return 0;
		if(row2>=regionsum.size()-1)
			row2=regionsum.size()-2;
		if(col2>=regionsum[0].size()-1)
			col2=regionsum[0].size()-2;
		if(row1<0)
			row1=0;
		if(col1<0)
			col1=0;
		return regionsum[row2+1][col2+1]+regionsum[row1][col1]-regionsum[row2+1][col1]-regionsum[row1][col2+1];
	}
};

int _tmain(int argc, _TCHAR* argv[])
{
	vector<vector<int>>matrix;
	vector<int>aa;
	//aa.push_back(5);
	//matrix.push_back(aa);
	NumMatrix numMatrix(matrix);
	cout<<numMatrix.sumRegion(0, 0, 2, 3);
	system("pause");
	return 0;
}

accepted