Dag 18 in MATLAB

clc
clear
close all

tic
disp('starting...')

x = importdata('input.txt');
s = x{1};
for i=2:size(x,1)
    s = addSnailfishNumbers(s,x{i});
end
M = getMagnitude(s);
disp(M);

% Part 2
maxM = -inf;
for i=1:size(x,1)
    for j=1:size(x,1)
        s = addSnailfishNumbers(x{i},x{j});
        M = getMagnitude(s);
        if M>maxM
            maxM=M;
        end
    end
end
disp(maxM)
toc
disp('Finished')

function s = addSnailfishNumbers(x,y)
s = ['[',x,',',y,']'];
s = reduceSnailfishNumber(s);
end

function y = reduceSnailfishNumber(s)
while 1
    sNew = explodeSnailfishNumber(s);
    if isequal(sNew,s)
        sNew = splitSnailfishNumber(s);
        if isequal(sNew,s)
            break
        end
        s = sNew;
    end
    s = sNew;
end
y=s;
end

function y=explodeSnailfishNumber(s)
L = getSnailfishNumberLevel(s);

if ~any(L==4) % nothing to explode, return the orginal number
    y=s;
    return
end

% Find positions of leftmost pair to explode
idxList     = find(L==4);
startIdx    = idxList(1);

z = find(diff(idxList)~=1, 1);
if isempty(z)
    endIdx = idxList(end);
else
    endIdx = idxList(z(1));
end

pairToExplode = s(startIdx:endIdx);

%% find the first number to the left of the pair to explode (if any);
leftNumberStr = [];
for i = startIdx-1:-1:1
    if s(i)>47 && s(i)<58 % 0..9
        leftNumberStr = s(i);
        leftNumberEndIdx = i;
        for j=i-1:-1:1
            if s(j)>47 && s(j)<58 % 0..9
                leftNumberStr = [s(j),leftNumberStr];
            else
                leftNumberStartIdx = j+1;
                break
            end
        end
        break
    end
end
if ~isempty(leftNumberStr)
    leftNumberVal = str2double(leftNumberStr);
end
%% find the first number to the right of the pair to explode (if any);
rightNumberStr = [];
for i = endIdx+1:length(s)
    if s(i)>47 && s(i)<58 % 0..9
        rightNumberStr = s(i);
        rightNumberStartIdx = i;
        for j=i+1:length(s)
            if s(j)>47 && s(j)<58 % 0..9
                rightNumberStr = [rightNumberStr,s(j)];
            else
                rightNumberEndIdx = j-1;
                break
            end
        end
        break
    end
end
if ~isempty(rightNumberStr)
    rightNumberVal = str2double(rightNumberStr);
end

%% Modify left/right numbers
pairValues = getPairValues(pairToExplode);

if ~isempty(rightNumberStr)
   % Add right value of exploded pair to the first number right of it:
   newRightVal = rightNumberVal + pairValues(2);
   newRightStr = num2str(newRightVal);
   s = [s(1:rightNumberStartIdx-1),newRightStr,s(rightNumberEndIdx+1:end)];
end

% replace exploding pair with '0'
s = [s(1:startIdx-1),'0',s(endIdx+1:end)];

if ~isempty(leftNumberStr)
   % Add left value of exploded pair the the first number left of it:
   newLeftVal = leftNumberVal + pairValues(1);
   newLeftStr = num2str(newLeftVal);
   s = [s(1:leftNumberStartIdx-1),newLeftStr,s(leftNumberEndIdx+1:end)];
end
y=s;
end

function s = splitSnailfishNumber(s)
% find numbers > 9 and split the leftmost of those numbers.
idxZeroToNine       = s>47 & s<58;
idxLargerThanNine   = strfind(idxZeroToNine,[1,1]); % i.e. at least 2 characters from 0-9 in a row.

if isempty(idxLargerThanNine)
    return %nothing to  split
else
    splitNumberStartIdx = idxLargerThanNine(1);
end

splitNumberStr = s(splitNumberStartIdx);
for k=splitNumberStartIdx+1:length(s)
    if s(k)>47 && s(k)<58
        splitNumberStr = [splitNumberStr,s(k)];
    else
        splitNumberEndIdx = k-1;
        break
    end
end

splitNumberVal      = str2double(splitNumberStr);
splitNumberVal1     = floor(splitNumberVal/2);
splitNumberVal2     = ceil(splitNumberVal/2);

splitNumberVal1Str  = num2str(splitNumberVal1);
splitNumberVal2Str  = num2str(splitNumberVal2);

replacementPair     = ['[',splitNumberVal1Str,',',splitNumberVal2Str,']'];
s = [s(1:splitNumberStartIdx-1),replacementPair,s(splitNumberEndIdx+1:end)];
end

function L=getSnailfishNumberLevel(s)
L = zeros(1,size(s,2));
currentLevel = -1;
for i=1:size(s,2)
    switch s(i)
        case '['
            currentLevel    = currentLevel + 1;
            L(i)            = currentLevel;
        case ']'
            L(i)            = currentLevel;
            currentLevel    = currentLevel - 1;
        otherwise
            L(i)            = currentLevel;
    end
end
end

function val = getPairValues(p)
val = [str2double(p(2:find(p==',')-1)),str2double(p(find(p==',')+1:end-1))];
end

function M = getMagnitude(s)
while 1
    L           = getSnailfishNumberLevel(s);
    maxDepth    = max(L);
    idxMaxDepth = find(L==maxDepth);
    startIdx    = idxMaxDepth(1);

    z           = find(diff(idxMaxDepth)~=1);
    if isempty(z)
        endIdx = idxMaxDepth(end);
    else
        endIdx = idxMaxDepth(z(1));
    end

    val         = str2num(s(startIdx:endIdx)); %#ok<ST2NM>
    newVal      = 3*val(1) + 2*val(2);
    newValStr   = num2str(newVal);
    s           = [s(1:startIdx-1),newValStr,s(endIdx+1:end)];
    if maxDepth==0
        break
    end
end
M=str2double(s);
end