#include <stdio.h>
 
// グローバル変数（rec の呼び出し回数を数える）
int c = 0;
 
// 例：a{n} = -6a{n-1} - 9a{n-2}, a1=1, a2=2
int rec(int n){
    c++;  // rec が呼ばれるたびにカウント
 
    if(n == 1) return 1;
    if(n == 2) return 2;
 
    return -6 * rec(n-1) - 9 * rec(n-2);
}
 
int main(void) {
    int n = 5;
 
    int ans = rec(n);
    printf("数列a%dの値は%d\n", n, ans);
    printf("このときrecの呼び出し回数は%d\n", c);
 
    return 0;
}
 

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