扔 n 个骰子，向上面的数字之和为 S。

Question

问题描述

扔 n 个骰子，向上面的数字之和为 S。给定 Given n，请列出所有可能的 S 值及其相应的概率。

样例

给定 n = 1，返回 [ [1, 0.17], [2, 0.17], [3, 0.17], [4, 0.17], [5, 0.17], [6, 0.17]]。

public class Solution {
    /**
     * @param n an integer
     * @return a list of Map.Entry<sum, probability>
     */
    public List<Map.Entry<Integer, Double>> dicesSum(int n) {
        // Write your code here
        // Ps. new AbstractMap.SimpleEntry<Integer, Double>(sum, pro)
        // to create the pair
    }
}

Answer 1

public class Solution {
    /**
     * @param n an integer
     * @return a list of Map.Entry<sum, probability>
     */
    public List<Map.Entry<Integer, Double>> dicesSum(int n) {
        // Write your code here
        // Ps. new AbstractMap.SimpleEntry<Integer, Double>(sum, pro)
        // to create the pair
         List<Map.Entry<Integer, Double>> results = 
                new ArrayList<Map.Entry<Integer, Double>>();
        
        double[][] f = new double[n + 1][6 * n + 1];
        for (int i = 1; i <= 6; ++i)
            f[1][i] = 1.0 / 6;

        for (int i = 2; i <= n; ++i)
            for (int j = i; j <= 6 * n; ++j) {
                for (int k = 1; k <= 6; ++k)
                    if (j > k)
                        f[i][j] += f[i - 1][j - k];

                f[i][j] /= 6.0;
            }

        for (int i = n; i <= 6 * n; ++i) 
            results.add(new AbstractMap.SimpleEntry<Integer, Double>(i, f[n][i]));

        return results;
    }
}

Answer 2

// 1.
List<Map.Entry<Integer, Double>> ret;
for (int i = n; i <= n * 6; i++) {
    ret[i] = 0;
}

// 2.
public void calc(int n, int arr[], List<Map.Entry<Integer, Double>> ret) {
    if (n == 0) {
        int s = sum(arr);
        ret[s]++;
        return;
    }
    for (int i = 0; i < 6; i++) {
        arr[n - 1] = i + 1;
        calc(n - 1, arr, ret);
    }
}

//3 统计总次数，在把每个值除以总和，再返回

代码只是粗略代码，仅供参考