leetcode 233: Number of Digit One
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Number of Digit One
Total Accepted: 307 Total Submissions: 1853Given an integer(整数) n, count the total number of digit(数字) 1 appearing in all non-negative(非负的) integers less than or equal to n.
For example:
Given n = 13,
Return 6, because digit 1 occurred in the following numbers: 1, 10, 11, 12, 13.
reference(参考): https://leetcode.com/discuss/44281/4-lines-o-log-n-c-Java-Python
intuitive(直觉的): 每10个数, 有一个个位是1, 每100个数, 有10个十位是1, 每1000个数, 有100个百位是1. 做一个循环, 每次计算单个位上1得总个数(个位,十位, 百位).
以算百位上1为例子: 假设百位上是0, 1, 和 >=2 三种情况:
case 1: n=3141092, a= 31410, b=92. 计算百位上1的个数应该为 3141 *100 次.
case 2: n=3141192, a= 31411, b=92. 计算百位上1的个数应该为 3141 *100 + (92+1) 次.
case 3: n=3141592, a= 31415, b=92. 计算百位上1的个数应该为 (3141+1) *100 次.
以上三种情况可以用 一个公式概括:
( + ) / * + ( % = ) * ( + );
[CODE]
- publicclass Solution {
- public countDigitOne(
- ones =
- ; m <= n; m *=
- a = n/m, b = n%m;
- ones += (a +
- ) ones += b +
- return ones;
public class Solution { public int countDigitOne(int n) { int ones = 0; for (long m = 1; m <= n; m *= 10) { long a = n/m, b = n%m; ones += (a + 8) / 10 * m; if(a % 10 == 1) ones += b + 1; } return ones; }}
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