【leetcode

文章目录

• URL
• 题目
• 分析
• 源码
• • 工程结构
  • 源码文件
  • LOG参考
• 源码概述
• 小结

URL

链接：https://leetcode-cn.com/problems/count-numbers-with-unique-digits/

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题目

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分析

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源码 工程结构

.
└── main_357.c

源码文件

/* main_357.c */
#include 

int count_num_with_unique_digits(int n){
    if (n == 0)
        return 1;
    if (n == 1)
        return 10;
    int ans = 10 , cur = 9;
    for (int i = 0; i < n - 1; i++){
        cur *= 9 - i;
        ans += cur;
    }
    return ans;
}

int main()
{
    for (int i = 0 ; i <= 10; ++i){
        printf("n = %d , \t count = %d\n",i,count_num_with_unique_digits(i));
    }

    return 0;
}

LOG参考

n = 0 ,          count = 1
n = 1 ,          count = 10
n = 2 ,          count = 91
n = 3 ,          count = 739
n = 4 ,          count = 5275
n = 5 ,          count = 32491
n = 6 ,          count = 168571
n = 7 ,          count = 712891
n = 8 ,          count = 2345851
n = 9 ,          count = 5611771
n = 10 ,         count = 8877691

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源码概述

1. C1/9 * C1/(9-1) *…*C1/(9-(n-1))，n∈[2,10]
2. 一个累乘的结果

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小结

1. 算法来源于生活