> [!Definition] > A [[Computational Problem]] where the answer for every instance is yes or no. > > [!Example] > **Input** - An array $A[1,2,\dots,n]$ of $n$ numbers. > **Output** > - Yes if there exists indices $i,j\in \{ 1,2,\dots n \}$ with $i\neq j$ such that $A[i]+A[j]=0$ > - No otherwise. # Complexity Classes - #### [[P]], - #### [[NP]], - See [[P versus NP]].