leetcode 552. Student Attendance Record II
又一题动态规划
public class Solution {
public int checkRecord(int n) {
final int MOD = 1000000007;
int[][][] f = new int[n+1][2][3];
// at most 1 A, at most 2 L
f[0] = new int[][]{{1, 1, 1}, {1, 1, 1}};
for(int i=1;i<=n;i++){
for(int j=0;j<=1;j++){
for(int k=0;k<=2;k++){
int val = f[i-1][j][2]; // ..p
if(j>0) val = (val + f[i-1][j-1][2])%MOD; // ..A
if(k>0) val = (val + f[i-1][j][k-1])%MOD; // ..L
f[i][j][k] = val; //
}
}
}
return f[n][1][2];
}
}
