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/**
* Your NumMatrix object will be instantiated and called as such:
* NumMatrix obj = new NumMatrix(matrix);
* int param_1 = obj.sumRegion(row1,col1,row2,col2);
*/
class NumMatrix {
public:
NumMatrix(vector<vector<int>> ma) :matrix(ma){
}
int sumRegion(int row1, int col1, int row2, int col2) {
int r1=row1,c1,r2=row2,c2=col2;
int sum=0;
for(;r1<=r2;r1++)
{
c1=col1;
for(;c1<=c2;c1++)
{
sum+=matrix[r1][c1];
}
}
return sum;
}
private:vector<vector<int>>matrix;
};
class NumMatrix {
private:
vector<vector<int>> dp;
public:
NumMatrix(vector<vector<int>> matrix) {
if (matrix.size() == 0 || matrix[0].size() == 0) {
return;
}
int n = matrix.size();
int m = matrix[0].size();
dp.resize(n + 1, vector<int>(m + 1, 0));
for (int r = 0; r < n; r++) {
for (int c = 0; c < m; c++) {
dp[r + 1][c + 1] = dp[r + 1][c] + dp[r][c + 1] + matrix[r][c] - dp[r][c];
}
}
}
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];
}
};
同样都是O(n2)的时间复杂度,它的时间是300ms 比我的快一倍 这是为什么 难道是因为他的循环在构造函数么?