sudoku_lowmode(xcell)

function output = sudoku_lowmode(xcell)
% Function: sudoku_lowmode
%           used for getting all number that just appears once in the cell
%           
% Input: xcell = 1x9 or 9x1 or 3x3 cell
% Output: output = 9x1 cell, each cell will contain the numbers that just
%         appears once in the corresponding cell in xcell 
% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% This is a sub-function of the sub-function sudoku_stage1
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% All copyrights reserved
% By Yue Wu
% 10/05/2009
% ECE Dept, Tufts Univ.
% MA, Medford 02155
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

for i = 1:9
    clear tmpcell
    tmpcell = xcell{i}; % each time, extract one cell in xcell
    % calculate the frequency for each possible number
    for j = 1:9
        flist(j) = length(find(tmpcell == j));
    end
    % find its lowest frequency
    minj = min(flist);
    if minj == 1 % if lowest frequency = 1, find all the numbers with this frequency
        output{i} = find(flist == minj);
    else % otherwise, return to empty list
        output{i} = [];
    end
end