15. Judge whether the target value exists in the two-dimensional array

public boolean findNumberIn2DArray(int[][] matrix, int target) {
        int i = matrix.length - 1, j = 0;
        while(i >= 0 && j < matrix[0].length) {
            if(matrix[i][j] > target) i--;
            else if(matrix[i][j] < target) j++;
            else return true;
        }
        return false;
    }

The idea is detailed on the paper