nowcoderD Xieldy And His Password

题意:一个01序列,长度1e6,问有多少子串十进制是3的倍数

题解:DP[i][j]代表前i个并且以i为结尾,且十进制%3==j的串的个数

#include<bits/stdc++.h>
#define maxn 1001000
using namespace std;
char s[maxn];
long long dp[maxn][3], sum;
int main(){while(~scanf("%s", s+1)){sum = 0;int l = strlen(s+1);for(int i=1;i<=l;i++){if(s[i] == '0'){dp[i][0] = dp[i-1][0]+1;dp[i][2] = dp[i-1][1];dp[i][1] = dp[i-1][2];}else{dp[i][0] = dp[i-1][1];dp[i][1] = dp[i-1][0]+1;dp[i][2] = dp[i-1][2];}sum += dp[i][0];}cout<<sum<<endl;}return 0;
}