What Word Break Leetcode Problem Taught Me About Debugging Order
I recently worked through the classic Word Break problem in an interview. My approach was solid from the start — recursion with memoization, a breakable helper that tests every prefix and recurses on the rest. The logic was right. What slowed me down was everything around the logic. Here's the solution I landed on: class Solution { public: bool wordBreak ( string s , vector < string >& wordDict ) { unordered_set < string > dict ( wordDict . begin (), wordDict . end ()); unordered_map < size_t , bool > memo ; return breakable ( s , dict , memo , 0 ); // missed: breakable was a free function defined below -> "not declared in this scope" } private : // missed: had int here, compared against s.length() (size_t) -> sign-compare warnings bool breakable ( const string & s , const unordered_set < string >& dict , unordered_map < size_t , bool >& memo , size_t starting ) { if ( starting == s . length ()) return true ; if ( memo . count ( starting )) return memo [ starting ]; for ( size_t e = starting + 1 ; e <= s . length (); e ++ ) { string word = s . substr ( starting , e - starting ); // missed: shadowed an outer `word`, and had substr(starting, e) instead of e - starting if ( dict . count ( word ) && breakable ( s , dict , memo , e )) { memo [ starting ] = true ; // missed: wrote == instead of =, so success was never cached return true ; } } memo [ starting ] = false ; // missed: this line, so failures were never cached and memoization broke down return false ; } }; The real lesson Most of what tripped me up was syntax and scope — a function declared in the wrong place, signed/unsigned mismatches, a shadowed variable, == where I meant = . None of these were about the algorithm. But because I spent my time chasing them, I had less room to focus on the one thing that actually matters in this problem: the logical correctness of the memoization. The takeaway I'm keeping: get the syntax and scoping clean early, so the debugging budget goes toward logic, not typos. That's the