43. 从 1 到 n 整数中 1 出现的次数.md

# 43. 从 1 到 n 整数中 1 出现的次数

[NowCoder](https://www.nowcoder.com/practice/bd7f978302044eee894445e244c7eee6?tpId=13&tqId=11184&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)

## 解题思路

```java
public int NumberOf1Between1AndN_Solution(int n) {
    int cnt = 0;
    for (int m = 1; m <= n; m *= 10) {
        int a = n / m, b = n % m;
        cnt += (a + 8) / 10 * m + (a % 10 == 1 ? b + 1 : 0);
    }
    return cnt;
}
```

> [Leetcode : 233. Number of Digit One](https://leetcode.com/problems/number-of-digit-one/discuss/64381/4+-lines-O(log-n)-C++JavaPython)