#include <stdio.h>
 
char decrypt_message(int n, char *s, char *q) {
    char result[n + 1];
    result[n] = '\0';
    for (int i = 0; i < n; i++) {
        int shift = (q[i] == 'U') ? (i + 1) : -(i + 1);
        int char_code = s[i] + shift;
        if (char_code < 'a') {
            char_code += 26;
        } else if (char_code > 'z') {
            char_code -= 26;
        }
        result[i] = char_code;
    }
    return *result;
}
 
int main() {
    int T;
    scanf("%d", &T);
    for (int t = 0; t < T; t++) {
        int n;
        scanf("%d", &n);
        char s[n + 1], q[n + 1];
        scanf("%s", s);
        scanf("%s", q);
 
        // Decrypt the message and print the result
        printf("%s\n", decrypt_message(n, s, q));
    }
    return 0;
}