PAT a1093题解

#include <cstdio>#include <cstring>const int MAXN = 100010;const int MOD = 1000000007;char str[MAXN];int leftNumP[MAXN] = {0};int main(){gets(str);int len = strlen(str);for(int i = 0; i < len; i++){if(i > 0){leftNumP[i] = leftNumP[i - 1];}if(str[i] == 'P'){leftNumP[i]++;}}int ans = 0, rightNumT = 0;for(int i = len - 1; i >= 0; i--){if(str[i] == 'T'){rightNumT++;}else if(str[i] == 'A'){ans = (ans + leftNumP[i] * rightNumT) % MOD;}}printf("%d", ans);return 0;}