JZ31 整数中1出现的次数

本文最后更新于：2022年4月9日 中午

image-20211008104718058

Solution

  • 利用规律
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class Solution {
public:
    int NumberOf1Between1AndN_Solution(int n) {
        long digit = 1;
        int high = n / 10, cur = n % 10, low = 0;
        int res = 0;
        
        while (high != 0 || cur != 0) {
            if (cur == 0) {
                res += high * digit;
            } else if (cur == 1) {
                res += high * digit + low + 1;
            } else {
                res += (high + 1) * digit;
            }
            low += cur * digit;
            cur = high % 10;
            high /= 10;
            digit *= 10;
        }
        return res;
    }
};