View Compilation Error

0_0_27748609_31889.cpp: In function 'int main()':
0_0_27748609_31889.cpp:19:18: error: 'a' was not declared in this scope
              if (a[i] != a[j]) dp[i][j] = max(dp[i+1][j], dp[i][j-1]);
                  ^
0_0_27748609_31889.cpp:19:69: error: 'max' was not declared in this scope
              if (a[i] != a[j]) dp[i][j] = max(dp[i+1][j], dp[i][j-1]);
                                                                     ^
0_0_27748609_31889.cpp:25:37: error: 'max' was not declared in this scope
           ans = max(ans,dp[i][i+n-1]);
                                     ^