Leetcode 题目解析之 Number of Digit One

Given an integer n, count the total number of digit 1 appearing in all non-negative 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.

Hint:

• Beware of overflow.

代码语言：javascript复制

    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;
    }

count integer numbers overflow

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