CDOJ 1135 邱老师看电影 概率dp

概率dp，推一个概率公式就行。i==2时那里写错了一个+-号，wa了两发

代码：

#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>#include <vector>#include <algorithm>using namespace std;#define maxn 1005double dp[maxn][maxn];int w, b;int main(){//freopen("input.txt", "r", stdin);scanf("%d%d", &w, &b);dp[0][0] = 0;for (int i = 1; i < maxn; ++i)dp[i][0] = 1, dp[0][i] = 0;for (int i = 1; i < maxn; ++i)dp[i][1] = i*1.0 / (i + 1);dp[1][2] = 1.0 / 3;for (int i = 2; i < maxn; ++i)dp[i][2] = i*1.0 / (i + 2) + 2.0 / (i + 2) / (i + 1);for (int i = 1; i < maxn; ++i){for (int j = 3; j < maxn; ++j){dp[i][j] = i*1.0 / (i + j) + j*1.0*(j - 1) / (i + j) / (i + j - 1)*((j - 2)*1.0 / (i + j - 2)*dp[i][j - 3] + i*1.0 / (i + j - 2)*dp[i - 1][j - 2]);}}printf("%.9f\n", dp[w][b]);//system("pause");//while (1);return 0;}