力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台

暴力

双层for循环，遍历子矩阵。

前缀和算法：

class NumMatrix {private int sum[][];private int matrix[][];public NumMatrix(int[][] matrix) {this.matrix=matrix;int rows=matrix.length+1;int cols=matrix[0].length+1;this.sum=new int[rows][cols];init(cols,rows);}public void init(int cols,int rows){for(int i=1;i<rows;i++){for(int j=1;j<cols;j++){this.sum[i][j]=this.sum[i-1][j]+this.sum[i][j-1]-this.sum[i-1][j-1]+this.matrix[i-1][j-1];}}}public int sumRegion(int row1, int col1, int row2, int col2) {return this.sum[row2+1][col2+1]-this.sum[row2+1][col1]-this.sum[row1][col2+1]+this.sum[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);*/