《剑指offer》第四十八题：最长不含重复字符的子字符串

Posted 2020-11-27 zsy-blog

// 面试题48：最长不含重复字符的子字符串
// 题目：请从字符串中找出一个最长的不包含重复字符的子字符串，计算该最长子
// 字符串的长度。假设字符串中只包含从‘a‘到‘z‘的字符。

#include <string>
#include <iostream>

// 方法一：蛮力法
bool hasDuplication(const std::string& str, int position[]);

int longestSubstringWithoutDuplication_1(const std::string& str)
{
    int length = str.length();
    int longest = 0;
    int* position = new int[26];  //26个字母

    for (int start = 0; start < length; ++start)
    {
        for (int end = start; end < length; ++end)
        {
            int count = end - start + 1;
            const std::string& substring = str.substr(start, count); //裁剪出子字符串
            if (!hasDuplication(substring, position))
            {
                if (count > longest)
                    longest = count;
            }
            else
                break;
        }
    }
    delete[] position;

    return longest;
}

bool hasDuplication(const std::string& str, int position[])
{
    for (int i = 0; i < 26; ++i)
        position[i] = -1;

    for (int i = 0; i < str.length(); ++i)
    {
        int indexInPosition = str[i] - ‘a‘;
        if (position[indexInPosition] >= 0)  //字符串出现过2次以上
            return true;

        position[indexInPosition] = indexInPosition;
    }

    return false;
}

// 方法二：动态规划
int longestSubstringWithoutDuplication_2(const std::string& str)
{
    int maxLength = 0;
    int curLength = 0;

    //每个字母上一次出现的位置
    int* position = new int[26];
    for (int i = 0; i < 26; ++i)
        position[i] = -1;

    for (int i = 0; i < str.length(); ++i)
    {
        int indexPrev = position[str[i] - ‘a‘];  //该字母上次出现的位置
        if (indexPrev < 0 || i - indexPrev > curLength)  //当前字母未出现过, 或上次出现在当前序列外
            ++curLength;
        else
        {
            if (curLength > maxLength)
                maxLength = curLength;

            curLength = i - indexPrev; //否则以当前字母上次出现的位置后到当前字母位置作为当前长度
        }
        position[str[i] - ‘a‘] = i;  //更新位置索引
    }
    
    if (curLength > maxLength)
        maxLength = curLength;

    delete[] position;

    return maxLength;
}

// ====================测试代码====================
void testSolution1(const std::string& input, int expected)
{
    int output = longestSubstringWithoutDuplication_1(input);
    if (output == expected)
        std::cout << "Solution 1 passed, with input: " << input << std::endl;
    else
        std::cout << "Solution 1 FAILED, with input: " << input << std::endl;
}

void testSolution2(const std::string& input, int expected)
{
    int output = longestSubstringWithoutDuplication_2(input);
    if (output == expected)
        std::cout << "Solution 2 passed, with input: " << input << std::endl;
    else
        std::cout << "Solution 2 FAILED, with input: " << input << std::endl;
}

void test(const std::string& input, int expected)
{
    testSolution1(input, expected);
    testSolution2(input, expected);
}

void test1()
{
    const std::string input = "abcacfrar";
    int expected = 4;
    test(input, expected);
}

void test2()
{
    const std::string input = "acfrarabc";
    int expected = 4;
    test(input, expected);
}

void test3()
{
    const std::string input = "arabcacfr";
    int expected = 4;
    test(input, expected);
}

void test4()
{
    const std::string input = "aaaa";
    int expected = 1;
    test(input, expected);
}

void test5()
{
    const std::string input = "abcdefg";
    int expected = 7;
    test(input, expected);
}

void test6()
{
    const std::string input = "aaabbbccc";
    int expected = 2;
    test(input, expected);
}

void test7()
{
    const std::string input = "abcdcba";
    int expected = 4;
    test(input, expected);
}

void test8()
{
    const std::string input = "abcdaef";
    int expected = 6;
    test(input, expected);
}

void test9()
{
    const std::string input = "a";
    int expected = 1;
    test(input, expected);
}

void test10()
{
    const std::string input = "";
    int expected = 0;
    test(input, expected);
}

int main(int argc, char* argv[])
{
    test1();
    test2();
    test3();
    test4();
    test5();
    test6();
    test7();
    test8();
    test9();
    test10();

    return 0;
}

测试代码

分析：动态规划，递归。