每天一道剑指offer-整数中1出现的次数

public int NumberOf1Between1AndN_Solution(int n) {    if(n < 1){        return 0;    }    int res = 0;    for(int i = 1 ; i <= n ; i++){        res += count(i);    }    return res;}
public int count(int n){    int count = 0;    while(n != 0){        //取个位        count = (n % 10 == 1) ? ++count : count;        //去掉个位        n /= 10;    }    return count;}

public int NumberOf1Between1AndN_Solution(int n) {    if(n < 1){        return 0;    }    return process(n);}
public int process(int n){    if(n == 0){        return 0;    }    if(n < 10 && n > 0){        return 1;    }    int res = 0;    //得到十进制位数    int bitCount = bitCount(n);    //十进制最高位上的数    int highestBit = numOfBit(n, bitCount);    //1、统计最高位为1时，共有多少个数    if(highestBit > 1){        res += powerOf10(bitCount - 1);    }else{        //highestBit == 1        res += n - powerOf10(bitCount - 1) + 1;    }    //2、统计其它位为1的情况    res += powerOf10(bitCount - 2) * (bitCount - 1) * highestBit;    //3、剩下的部分交给递归    res += process(n % powerOf10(bitCount - 1));    return res;}
//返回10的n次方public int powerOf10(int n){    if(n == 0){        return 1;    }    boolean minus = false;    if(n < 0){        n = -n;        minus = true;    }    int res = 1;    for(int i = 1 ; i <= n ; i++){        res *= 10;    }    return minus ? 1 / res : res;}
public int bitCount(int n){    int count = 1;    while((n /= 10) != 0){        count++;    }    return count;}
public int numOfBit(int n, int bit){    while(bit-- > 1){        n /= 10;    }    return n % 10;}