Compute the probability of a Republican majority - EPI

Compute the probability of a Republican majority

House_majority.cpp HouseMajority.java
  public static double houseMajority(double[] prob, int n) {
    // Initializes DP table.
    double[][] P = new double[n + 1][n + 1];
    for (double[] element : P) {
      Arrays.fill(element, -1.0);
    }

    // Accumulates the probabilities of majority cases.
    double probSum = 0.0;
    for (int r = (int) ceil(0.5 * n); r <= n; ++r) {
      probSum += houseMajorityHelper(prob, r, n, P);
    }
    return probSum;
  }

  // prob is the probability that each Republican wins.
  // r is the number of Republicans wins, and n is the number of elections.
  private static double houseMajorityHelper(double[] prob, int r, int n,
                                            double[][] P) {
    if (r > n) {
      return 0.0; // Base case: not enough Republicans.
    } else if (r == 0 && n == 0) {
      return 1.0; // Base case.
    } else if (r < 0) {
      return 0.0;
    }

    if (P[r][n] == -1.0) {
      P[r][n] = houseMajorityHelper(prob, r - 1, n - 1, P) * prob[n - 1]
          + houseMajorityHelper(prob, r, n - 1, P) * (1.0 - prob[n - 1]);
    }
    return P[r][n];
  }