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cpp -get sum of range

Milan Niroula answered on September 26, 2022 Popularity 3/10 Helpfulness 1/10

answer cpp -get sum of range

cpp -get sum of range

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class NumMatrix {

    int[][] mat;
    int[][] matSum;
    public NumMatrix(int[][] matrix) {
        this.mat = matrix;
        preCalc();
    }
    
    private int getMatSum(int i, int j) {
        if(i<0 || j<0)
            return 0;
        else
            return matSum[i][j];
    }
    
    /*
    *
    *   2       3
        7       1
    *   
    *   Trying to get the sum of above matrix in the right botom corner, so the way would be :   
    *
    *   2       2+3
        2+7     (2+3)+(2+7)+1-2
    *
    *   Adding top sum and left sum and current value, subtracting top left sum value
    */
    
    private void preCalc(){
        matSum = new int[mat.length][mat[0].length];
        for(int i = 0; i<mat.length; i++){
            for(int j=0; j<mat[0].length; j++){
                matSum[i][j] = getMatSum(i-1,j) + getMatSum(i, j-1) + mat[i][j] - getMatSum(i-1, j-1);
            }
        }
    }
        
    /*
    *
    *   Now since sum has been calculated already in matSum
    *   We will use it to calculate sum of region
    *   Sum of region will be :
            matSum[row2][col2] - getMatSum(row1-1, col2) - getMatSum(row2, col1-1) + getMatSum(row1-1, col1-1)
    *   
    *       
    *       matSum[row2][col2] : current value of matSum in lower bound of required region (row2, col2)
    *       getMatSum(row1-1, col2) : subtracting the block's sum above required region
    *       getMatSum(row2, col1-1) : subtracting the block's sum left to the required region
    *       getMatSum(row1-1, col1-1) : the intersection block, top left has been subtracted twice, adding again 1 time
    *
    *
    */
    
    public int sumRegion(int row1, int col1, int row2, int col2) {
        return matSum[row2][col2] - getMatSum(row1-1, col2) - getMatSum(row2, col1-1) + getMatSum(row1-1, col1-1);
    }
}

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

Popularity 3/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: java range sum

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Contributed on Sep 26 2022

Milan Niroula

0 Answers Avg Quality 2/10

cpp -get sum of range

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