查找小于输入数字的最大阶乘答案

【问题标题】：Finding the largest factorial that is less than the number entered查找小于输入数字的最大阶乘
【发布时间】：2020-11-01 17:32:35
【问题描述】：

基本上我希望我的代码做的是将阶乘结果与输入的数字进行比较，以找到小于输入数字的最大阶乘。由于某种原因，它没有打印任何内容。

public class Main {
  public static void main(String[] args) {
     int numinput = 150; //number than we are trying to find the largest factorial less than
     int num = 1; //number than we are solving a factorial for, to test against numinput
     int factorial = 1; //actual result of the factorial
     while (factorial < numinput) //finds the factorial of num
       for(int i = 1; i <= num; i++) {
         factorial *= i;
       }
     num++;
     if (factorial > numinput) {
        num--;
        System.out.println("The largest factorial less than " + numinput + "is !" + factorial);
     }
  }
}

【问题讨论】：

标签： java numbers factorial

【解决方案1】：

while 循环没有花括号，所以循环体中唯一的东西是for 循环。 num 从 1 开始，循环中的任何内容都不会增加它，所以它会永远循环。

不过，您不需要嵌套循环 - 一个计算阶乘的循环就足够了：

int numinput = 150; //number than we are trying to find the largest factorial less than
int num = 1;
int factorial = 1;

while (factorial < numinput) {
    num++;
    factorial *= num;
}

// We overshot to terminate the loop, go back one number
factorial /= num;
num--;

System.out.println
    ("The largest factorial less than " + numinput + " is " + num + "!, or " + factorial);

【讨论】：

【解决方案2】：

那是因为你的代码无法跳出这个while循环-

while (factorial < numinput) //finds the factorial of num
       for(int i = 1; i <= num; i++) {
         factorial *= i;
       }

由于您没有在 while 循环中使用括号，因此它刚刚获得了 for 循环，并且由于 num 的值永远不会增加，它会一直将 factorial 永远乘以 1。我想你想这样做 -

public class Main {
  public static void main(String[] args) {
     int numinput = 150; //number than we are trying to find the largest factorial less than
     int num = 1; //number than we are solivng a factorial for, to test agaisnt numinput
     int factorial = 1; //actual result of the factorial
     while (factorial < numinput) {
        for(int i = 1; i <= num; i++) {
            factorial *= i;
        }
        num++;
        if (factorial > numinput) {
            num--;
            System.out.println("The largest factorial less than " + numinput + "is !" + factorial);
        }
     }
  }
}

但是我检查了你的代码输出为 150，它是不正确的。我在下面提供我的代码 -

public class Main {
  public static void main(String[] args) {
     int numinput = 150; //number than we are trying to find the largest factorial less than
     int num = 1; //number than we are solivng a factorial for, to test agaisnt numinput
     int factorial = 1; //actual result of the factorial
     while (factorial <= numinput) {    // continue multiplying even if equal
        factorial = 1;
        for(int i = 1; i <= num; i++) {
            factorial *= i;
        }
        num++;
     }
    // now the factorial is surely greater than numinput, and it is the factorial of
    // current value of num - 1, we can remove the conditional
    // and reduce the factorial by num -1 since multiplying by num - 1 has
    // made it bigger than numinput
    factorial /= (num - 1);
    System.out.println("The largest factorial less than " + numinput + "is !" + factorial);
  }
}

【讨论】：

【解决方案3】：

我假设您说的是小于输入阶乘的最小整数阶乘。所以，代码应该是这样的：


public static void main(String[] args) {
    int input = 150; // example 
    for (int i = 1; i <= input - 1; i++) {
    int sum = (input - 1) * 1;
    }

    System.out.println(input);
}

【讨论】：