View Compilation Error

0_0_25396510_9270.cpp: In function 'void build()':
0_0_25396510_9270.cpp:52:27: error: 'stk' was not declared in this scope
         while (k > 0 && a[stk[k - 1]] > a[i]) --k;
                           ^
0_0_25396510_9270.cpp:53:18: error: 'stk' was not declared in this scope
         if (k) r[stk[k - 1]] = i;
                  ^
0_0_25396510_9270.cpp:54:29: error: 'stk' was not declared in this scope
         if (k < top) l[i] = stk[k];
                             ^
0_0_25396510_9270.cpp:55:9: error: 'stk' was not declared in this scope
         stk[k++] = i;
         ^