题目描述

这个比下面的快很多

样例

class Solution {
    public int numberOf1Between1AndN_Solution(int n) {
          int res=0;
        int temp=1;
        int ans=n;
        while (ans!=0){
            int yushu=ans%10;
             ans=ans/10;
             int item=n%temp;
            if (yushu==0)
                res+=ans*temp;
            else if (yushu==1)
            {
                res+=(ans*temp+item+1);
            }
            else res+=(ans+1)*temp;

            temp*=10;
        }
        return res;
    }
}

算法1

(暴力枚举) $O(n^2)$

blablabla

时间复杂度

参考文献

java 代码

class Solution {
    public int numberOf1Between1AndN_Solution(int n) {
         String s = "" + n;
        String[] item = s.split("");
        int count = 0;
        for (int i = 0; i < item.length; i++) {
            if (i!=0)
            count = count + Integer.valueOf(s.substring(0, i)) * (int) Math.pow(10, item.length - i - 1);
            if (Integer.valueOf(item[i]) != 0) {
                if (i==item.length-1)
                    count++;
                else{
                    if (Integer.valueOf(item[i]) == 1){
                        StringBuilder sb2 = new StringBuilder(s.substring(i));
                        sb2.deleteCharAt(0);
                        count = count + Integer.valueOf(sb2.toString()) + 1;
                    }
                    else
                        count=count +  (int) Math.pow(10, item.length - i - 1);

                }
            }

        }
        return count;
    }
}