面试宝典：字符串基础

内容来自：面试宝典 字符串章节

• 字符串与数字的相互转换
• 实现strcopy
• 求一个字符串中连续出现次数最多的子串
• 求一个字符串中相同且最长的子串
• 实现strstr
• 将一句话中的单词进行倒置，标点符号不变。比如一句话：i come from tiamjin. 倒换后称为 tianjin. from come i
• 计算从1-n之间的中包含1个个数
• 转变字符串格式为原来字符串里的字符+该字符出现的次数的个数

/*
 * mystring.h
 *
 *  Created on: Mar 10, 2017
 *      Author: wxquare
 */

#ifndef MYSTRING_H_
#define MYSTRING_H_

#include <cassert>
#include <string>
#include <iostream>

namespace MYSTRING {

void itoa(int val, char* str) {

    char* tmp = new char[10];

    int i = 0;
    while (val) {
        tmp[i++] = (val % 10) + '0';
        val = val / 10;
    }
    i = i - 1;
    int j = 0;
    while (i >= 0) {
        str[j++] = tmp[i--];
    }
    delete[] tmp;
}

int atoi(char* str) {

    int i = 0, res = 0;
    while (str[i] != '') {
        res = res * 10 + str[i++] - '0';
    }
    return res;
}

char* strcopy(char* strDest, const char* strSrc) {

    assert(strDest != nullptr && strSrc != nullptr);

    char* p = strDest;
    char* q = const_cast<char*>(strSrc);
    while (*q != '') {
        *p++ = *q++;
    }
    *p = '';  //notice
    return strDest;
}

/*
 * 求一个字符串中连续出现次数最多的字串
 * maximum number of consecutive strings in a string.
 */
std::string maxCounSubStr(const std::string &str) {
    int len = str.length();
    std::string res = str.substr(0, 1);
    int maxCount = 1, count;
    for (int i = 0; i < len; i++) {
        for (int j = i + 1; j < len; j++) {
            int offset = j - i;
            if (str.substr(i, offset) == str.substr(j, offset)) {
                count = 2;
                for (int k = j + offset; k < len; k += offset) {
                    if (str.substr(i, offset) == str.substr(k, offset)) {
                        count++;
                    } else {
                        break;
                    }
                }
                if (count > maxCount) {
                    maxCount = count;
                    res = str.substr(i, offset);
                }
            }
        }
    }
    return res;
}

/*
 * 求一个字符串中相同且最长的字串
 */
using string = std::string;
string sameAndLongestSubstr(const string& str) {
    string res;
    int len = str.length();
    bool isfound = false;
    for (int l = len; l >= 1; l--) {
        if (isfound)
            break;
        for (int i = 0; i < len; i++) {
            if (i + l < len) {
                string subStr = str.substr(i, l);
                if (str.find(subStr) != str.rfind(subStr)) {
                    res = subStr;
//                    std::cout << subStr << '	' << i << std::endl;
                    isfound = true;
                    break;
                }
            }
        }
    }
    return res;
}

/*
 * implement strstr
 * char * strstr ( const char * str1, const char * str2 );
 */
char* strstr(const char* str1, const char* str2) {
    char *cur = const_cast<char*>(str1);
    char *p1, *p2;
    while (cur != '') {
        p1 = cur;
        p2 = const_cast<char*>(str2);
        if (*p1 == *p2) {
            while (*p2 != '' && *p1 != '' && *p1++ == *p2++)
                ;
            if (*p2 == '')
                return cur;
            else if (*p1 == '')
                return NULL;
            else {
                cur++;
            }
        } else {
            cur++;
        }
    }
    return NULL;
}

/*
 * 把一句话里面的单词进行倒置
 * eg. "i come from tianjin."
 *        "tianjin. from come i"
 */
void reverseWords(string& sentence) {
    int len = sentence.length();
    char* tmp = new char[len];

    //整体倒置
    int i = len - 1, j = 0;
    while (i >= 0) {
        tmp[j++] = sentence[i--];
    }

    //每个单词的逆序
    int k = 0;
    i = 0, j = 0;
    while (i < len) {
        for (int j = i; j < len; j++) {
            if (tmp[j] == ' ' || j == len - 1) {
                if (j != len - 1) {
                    int n = j - i;
                    i = j + 1;
                    while (n--) {
                        sentence[k++] = tmp[--j];
                    }
                    sentence[k++] = ' ';
                } else {
                    int n = j - i + 1;
                    i = j + 1;
                    while (n--) {
                        sentence[k++] = tmp[j--];
                    }
                }
                break;
            }
        }
    }
    delete [] tmp;
}


/*
 * 统计1的个数
 * ege: f(13) = 6  {1,2,3,4,5,6,7,8,9,10,11,12,13}
 *
 */
int countOne(int n){
    if(n == 1) return 1;
    int r = n;
    int count = 0;
    while(r){
        if(r % 10 == 1){
            count++;
        }
        r = r / 10;
    }
    return countOne(n-1) + count;
}


/*
 * 把字符串转为字符加上数字的表述方式
 * ege： 1233444  转变为 11213243
 *
 */
string CharNumber(const string& str){
    string res;
    int len = str.length();
    int count = 1;
    for(int i=0;i<len;i++){
        if(i+1 < len && str[i+1] == str[i]){
            count++;
        }else{
            res.push_back(str[i]);
            res.push_back(count+'0');
            count = 1;
        }
    }
    return res;
}

}
;

#endif /* MYSTRING_H_ */