OneBitInNumSeq.java

package swordPointOffer;

/**
 * @Author: Wenhang Chen
 * @Description:
 * @Date: Created in 9:27 4/17/2020
 * @Modified by:
 */
public class OneBitInNumSeq {
    public int findNthDigit(int n) {
        if (n < 10) return n;
        //计算当前范围有几位数字 如10-99 有90*power位 power = 2
        int count = 0;
        int power = 1;
        while (true) {
            count = helper(power);
            //n在count这个范围内
            if (n < count) break;
            n -= count;
            power++;
        }
        //计算计数到的这个数字
        //Math.pow(10,power-1) -- 起始数字 n/power -- 剩余补充数字
        int resNum = (int) (Math.pow(10, power - 1) + n / power);
        return String.valueOf(resNum).charAt(n % power) - '0';
    }

    public int helper(int power) {
        if (power == 1) return 10;
        return (int) (Math.pow(10, power - 1) * 9 * power);
    }

}