View Compilation Error

0_0_2139004_18778.cpp: In function `int solve(Trie*, int, int, int, int)':
0_0_2139004_18778.cpp:117: error: `prev' undeclared (first use this function)
0_0_2139004_18778.cpp:117: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_2139004_18778.cpp: In function `int main()':
0_0_2139004_18778.cpp:170: error: `vs' undeclared (first use this function)