gcc - C++ recursion segfault. Can you help me see what I'm doing wrong? -

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this first time i've used recursion other find factorial of number. i'm building program find words in boggle board. following function resulting in segfaults:

void findword(vector<string>& board, set<string>& dictionary,           string prefix, int row, int column){   prefix += gettile(board, row, column);   if(prefix.length() > biggestwordlength)     return;   if(isoutofbounds(row, column))     return;   if(isword(prefix, dictionary) == 1)     foundwords.insert(prefix);   if(isword(prefix, dictionary) == 0)     return;   //note: not prevent using same tile twice in word   findword(board, dictionary, prefix, row-1, column-1);   findword(board, dictionary, prefix, row-1, column);   findword(board, dictionary, prefix, row-1, column+1);   findword(board, dictionary, prefix, row, column-1);   findword(board, dictionary, prefix, row, column+1);   findword(board, dictionary, prefix, row+1, column-1);   findword(board, dictionary, prefix, row+1, column);   findword(board, dictionary, prefix, row+1, column+1); }

you recursing in directions in cases. consider reduced recursion version:

void findword(... int x, int y, ...) {    ...    findword(... x, y+1, ...);    findword(... x, y-1, ...);    ... }

now consider when called x == 5 , y == 5 (for example, other position good). using indentation below represent nested calls:

findword(... 5, 5, ...)    findword(..., 5, 6, ...)    // x, y+1       ...    findword(..., 5, 5, ...)    // x, y-1       // ouch! same before, eventually:       findword(..., 5, 6, ...)       findword(..., 5, 5, ...)           // ouch!... here again! shall continue?

now, think algorithm. when looking word, first select first character, direction , test going in that direction how many letters can make word. algorithm implemented attempts find words not in lines in random shape.


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