面试题 32: 从1到n 整数中1出现的次数

一. 题目

输入一个整数n,求从1到n这n个整数的十进制表示中1出现的次数.例如输入12,从1到12这些整数中包含1的数字有1,10,11和12,1一共出现了5次.

代码请到我的代码库中下载 Point2Offer

二. 代码

package week_3;/**难度系数:***** * 剑指offer: 从1到n整数中1出现的次数 * 方法: 数字规律 * 测试用例:功能测试(0,1(边界值),5,99,10000(大数)) * @author dingding * Date:2017-6-28 13:25 * Declaration: All Rights Reserved! */public class No32 {    public static void main(String[] args) {        test1();        test2();        test3();        test4();        test5();        test6();    }    //solution    private static int findAllOf1From1ToN(int n){        if (n<=0) {            return 0;        }        String value = n+"";  //整数转为字符串        int[] numbers = new int[value.length()];        for (int i=0;i<numbers.length;i++){            numbers[i] = value.charAt(i)-'0';  //字符转数字        }        return numberOf1(numbers,0);    }    //统计1出现次数,递归    private static int numberOf1(int[] numbers, int curIndex) {        if (numbers == null || curIndex>=numbers.length||curIndex<0) {            return 0;        }        int first = numbers[curIndex];  // 待处理的第一个数字        int length = numbers.length - curIndex;  //所在位数        if (length == 1 && first == 0) {            return 0;        }        if (length == 1 && first>0) {            return 1;        }        int numFirstDigit = 0;        if (first>1) {            numFirstDigit = powerBase10(length-1);        }else if (first==1) {            numFirstDigit = atoi(numbers,curIndex+1)+1;        }        int numOtherDigits = first * (length-1) * powerBase10(length-2);        int numRecursive = numberOf1(numbers, curIndex+1);        return numFirstDigit+numOtherDigits+numRecursive;    }    //数字数组转换为数值    private static int atoi(int[] numbers, int i) {        int result = 0;        for (int j=i;j<numbers.length;j++){            result = (result*10+numbers[j]);        }        return result;    }    //求10的n次方    private static int powerBase10(int n) {        int result = 1;        for (int i=0;i<n;i++){            result *=10;        }        return result;    }    /*=====================测试用例======================*/    private static void test1() {         System.out.println(findAllOf1From1ToN(1)); // 1            }    private static void test2() {        System.out.println(findAllOf1From1ToN(0)); // 0         }    private static void test3() {        System.out.println(findAllOf1From1ToN(10)); // 2                }    private static void test4() {        System.out.println(findAllOf1From1ToN(55));             }    private static void test5() {        System.out.println(findAllOf1From1ToN(10000));      }    private static void test6() {        System.out.println(findAllOf1From1ToN(21345));              }}

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有不妥当之处,麻烦告知:D