class Solution {
public int digitAtIndex(int n) {
int dig=1;
int start=1;
int count=9;
while(n-count>0){
n-=count;
dig++;
start*=10;
count=start*9*dig;
}
long num=start+(n-1)/dig;
return Long.toString(num).charAt((n-1)%dig)-'0';
}
}
测试数据加强了,现在需要把 count 和 start 也变成 long 才能过测试