【每日算法Day 95】美团笔试题：四面体方案个数

#include <bits/stdc++.h>using namespace std;typedeflonglongll;constintmod=1e9+7;constintN=1000010;
lldp[N][2];
intmain() {    intk;  
scanf("%d", &k);   
memset(dp, 0, sizeofdp);  
dp[0][0] =1; 
for (inti=1; i<=k; ++i) {   
dp[i][0] = (dp[i-1][1] *3) %mod;   
dp[i][1] = (dp[i-1][1] *2+dp[i-1][0]) %mod;  
            }   
printf("%lld\n", dp[k][0]);  
return0;
           }

#include <bits/stdc++.h>using namespace std;typedeflonglongll;constintmod=1e9+7;constintN=1000010;
lldp[2];
intmain() {  
intk;  
scanf("%d", &k);   
dp[0] =1;    dp[1] =0; 
for (inti=1; i<=k; ++i) {  
inta= (dp[1] *3) %mod;   
intb= (dp[1] *2+dp[0]) %mod;  
dp[0] =a;      
dp[1] =b;    
            }    
printf("%lld\n", dp[0]); 
return0;
           }