Check for both sides adjacent elements that both must be less or both must be greater than current element
for ( int i = 1 ; i < n - 1 ; i ++ ) { if ( ( a [ i ] > a [ i - 1 ] && a [ i + 1 ] < a [ i ] ) || ( a [ i ] < a [ i - 1 ] && a [ i + 1 ] > a [ i ] ) )