Efficient Matrix Summation With O(1) Time Complexity

Problem
TC: O(n*m) for creating the prefix[][] sum matrix, O(row1+row2) for calculating the sum of the given rectangle
SC: O(n*m) for using the prefix[][] sum matrix

class NumMatrix {
    int prefix[][];
    public NumMatrix(int[][] matrix) {
        prefix = new int[matrix.length][matrix[0].length];
        for(int i=0;i<matrix.length;i++){
            int current = 0;
            for(int j = 0;j<matrix[0].length;j++){
                current+=matrix[i][j];
                prefix[i][j] = current;
            }
        }
    }
    public int sumRegion(int row1, int col1, int row2, int col2) {...