剑指 Offer 43. 1～n 整数中 1 出现的次数【力扣】

题意链接

给定一个数n，求1到n这些数中1出现的次数。

问题分析

动规

有点难，问题转化为每一个位出现的次数。

其他

链接

class Solution {
public:
    int countDigitOne(int n) {
        long long i = 1, coef = 1, sum = 0, cur_sum = 0;
        if (n < 10) return 1;
        while(coef <= n) {     
            cout << n << endl;       
            //cout << "n coef " << n << 't' << coef << endl;
            //cout << (n / (coef * 10)) * coef << endl;
            //cout << max(n % (coef * 10) - coef, 0) << endl;
            sum += (n / (coef * 10)) * coef + min(max(n % (coef * 10) - coef+1, 0LL), coef);
            //cur=n % 10;
            coef = coef * 10;
            //cout << "sum " << sum << endl;
        }
        return sum;
    }
};