HDU 3853 LOOPS 概率dp入门 (1)
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/*** Author : johnsondu*time: 2012-10-13-9:30 around*url: http://acm.hdu.edu.cn/showproblem.php?pid=3853*stratege: 概率dp**/#include <iostream>#include <cstdio>#include <cmath>#include <algorithm>#include <cstring>using namespace std ;#define eps 1e-10#define M 1005double dp[M][M] ;double p[M][M][3] ; // 三维,因为每个当前位置有3种走法(当前位置[r][c]),[r][c], [r+1][c], [r][c+1] ;int r, c ;double Abs (double t){return t < 0 ? -t : t ;}int main (){int i, j, k ;while (scanf ("%d%d", &r, &c) != EOF){for (i = 0; i < r; i ++)for (j = 0; j < c; j ++){for (k = 0; k < 3; k ++)scanf ("%lf", &p[i][j][k]) ; //0--[r][c], 1--[r][c+1], 2--[r+1][c]dp[i][j] = 0 ;}//dp[i][j] = p[i][j][0]*dp[i][j] + p[i][j][1] * dp[i][j+1] + p[i][j][2]*dp[i+1][j] + 2// --> dp[i][j] = (p[i][j][1] * dp[i][j+1] + dp[i+1][j]*p[i][j][2] + 2) / (1-p[i][j][0])// 注意: 1-p[i][j][0] > 0 ;for (i = r-1; i >= 0; i --)for (j = c-1; j >= 0; j --){if (i == r-1 && j == c-1) continue ;if (Abs (1-p[i][j][0] < eps)) continue ;dp[i][j] = (p[i][j][1] * dp[i][j+1] + dp[i+1][j]*p[i][j][2] + 2) / (1-p[i][j][0]) ;}printf ("%.3lf\n", dp[0][0]) ;}return 0 ;}
