Solved problem SRM339-D1-500 from TopCoder

Author: AliOsm

TopCoder/README.md

@@ -10,6 +10,7 @@
 - [SRM319-D1-500](http://community.topcoder.com/stat?c=problem_statement&pm=6714&rd=9999)
 - [SRM335-D1-500](https://community.topcoder.com/stat?c=problem_statement&pm=7337&rd=10659)
 - [SRM338-D1-500](https://community.topcoder.com/stat?c=problem_statement&pm=7289&rd=10662)
+- [SRM339-D1-500](https://community.topcoder.com/stat?c=problem_statement&pm=7422&rd=10663)
 - [SRM391-D1-500](https://community.topcoder.com/stat?c=problem_statement&pm=8202&rd=11125)
 - [SRM394-D2-1000](http://community.topcoder.com/stat?c=problem_statement&pm=8547&rd=11128)
 - [SRM458-D2-500](http://community.topcoder.com/stat?c=problem_statement&pm=10726&rd=14180&rm=&cr=14970299)

TopCoder/SRM339-D1-500.cpp

@@ -0,0 +1,39 @@
+/*
+  Idea:
+    - Dynamic Programming.
+    - dp[sum][rem][cur]:
+      `sum` represents the current money we have.
+      `rem` represents the remaining rounds we have.
+      `cur` represents the number of rounds we had lose.
+    - In each step we calculate the summation of the probability
+      of winning or lossing the current round.
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+double dp[1001][51][51];
+
+class TestBettingStrategy {
+  double rec(int sum, int rem, int cur, int &gol, double prb) {
+    if(sum >= gol)
+      return 1;
+    if(sum <= 0 || rem <= 0 || pow(2, cur) > sum)
+      return 0;
+
+    double &ret = dp[sum][rem][cur];
+    if(ret == ret)
+      return ret;
+    ret = 0;
+
+    return ret = prb * rec(sum + pow(2, cur), rem - 1, 0, gol, prb) +
+                 (1.0 - prb) * rec(sum - pow(2, cur), rem - 1, cur + 1, gol, prb);
+  }
+
+public:
+  double winProbability(int initSum, int goalSum, int rounds, int prob) {
+    memset(dp, -1, sizeof dp);
+    return rec(initSum, rounds, 0, goalSum, 1.0 * prob / 100.0);
+  }
+};