hdu 4849 Professor Tian（dp）

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题目链接：hdu 4849 Professor Tian

解题思路

将20位分开考虑，考虑最后为1的概率。

代码

#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>using namespace std;const int maxn = 205;double P[maxn], dp[maxn][2];int N, A[maxn];char sig[maxn][2];double solve (int bit, double s) {    dp[0][0] = 1 - s, dp[0][1] = s;    for (int i = 1; i <= N; i++) {        for (int j = 0; j < 2; j++)            dp[i][j] = dp[i-1][j] * P[i];        double p = 1 - P[i];        int v = (A[i]>>bit)&1;        if (sig[i][0] == '&') {            dp[i][v&0] += dp[i-1][0] * p;            dp[i][v&1] += dp[i-1][1] * p;        } else if (sig[i][0] == '|') {            dp[i][v|0] += dp[i-1][0] * p;            dp[i][v|1] += dp[i-1][1] * p;        } else {            dp[i][v^0] += dp[i-1][0] * p;            dp[i][v^1] += dp[i-1][1] * p;        }    }    return dp[N][1];}int main () {    int cas = 1, s;    while (scanf("%d", &N) == 1) {        scanf("%d", &s);        for (int i = 1; i <= N; i++) scanf("%d", &A[i]);        for (int i = 1; i <= N; i++) scanf("%s", sig[i]);        for (int i = 1; i <= N; i++) scanf("%lf", &P[i]);        double ans = 0;        for (int i = 0; i <= 20; i++)            ans += solve(i, (s>>i)&1) * (1<<i);        printf("Case %d:\n%.6lf\n", cas++, ans);    }    return 0;}

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