備戰秋招——算法與數據結構（6）

● 請你手寫代碼：最長公共連續子序列

參考回答：

int substr(string & str1, string &str2)
{
int len1 = str1.length();
int len2 = str2.length();
vector<vector<int>>dp(len1,vector<int>(len2,0));
for (int i = 0; i < len1; i++)
{
dp[i][0] = str1[i]==str1[0]?1:0;
}
for (int j = 0; j <= len2; j++)
{
dp[0][j] = str1[0]==str2[j]?1:0;
}
for (int i = 1; i < len1; i++)
{
for (int j = 1; j < len2; j++)
{
if (str1[i] == str2[j])
{
dp[i][j] = dp[i - 1][j - 1]+1;
}
}
}
int longest = 0;
int longest_index = 0;
for (int i = 0; i < len1; i++)
{
for (int j = 0; j < len2; j++)
{
if (longest < dp[i][j])
{
longest = dp[i][j];
longest_index = i;
}
}
}

//字符串爲從第i個開始往前數longest個

for (int i = longest_index-longest+1; i <=longest_index; i++)
{
cout << str1[i] << endl;
}
return longest;
}

● 手寫代碼：求一個字符串最長迴文子串

參考回答：

int LongestPalindromicSubstring(string & a)
{
int len = a.length();
vector<vector<int>>dp(len, vector<int>(len, 0));
for (int i = 0; i < len; i++)
{
dp[i][i] = 1;
}
int max_len = 1;
int start_index = 0;
for (int i= len - 2; i >= 0; i--)
{
for (int j = i + 1; j < len; j++)
{
if (a[i] == a[j])
{
if (j - i == 1)
{
dp[i][j] = 2;
}
else
{
if (j - i > 1)
{
dp[i][j] = dp[i + 1][j - 1] + 2;
}
}
if (max_len < dp[i][j])
{
max_len =  dp[i][j];
start_index = i;
}
}
else
{
dp[i][j] = 0;
}
}
}
cout << "max len is " << max_len << endl;
cout << "star index is" << start_index << endl;
return max_len;
}

● 手寫代碼：查找最長迴文子串

參考回答：

int LongestPalindromicSubstring(string & a)
{
int len = a.length();
vector<vector<int>>dp(len, vector<int>(len, 0));
for (int i = 0; i < len; i++)
{
dp[i][i] = 1;
}
int max_len = 1;
int start_index = 0;
for (int i= len - 2; i >= 0; i--)
{
for (int j = i + 1; j < len; j++)
{
if (a[i] == a[j])
{
if (j - i == 1)
{
dp[i][j] = 2;
}
else
{
if (j - i > 1)
{
dp[i][j] = dp[i + 1][j - 1] + 2;
}
}
if (max_len < dp[i][j])
{
max_len =  dp[i][j];
start_index = i;
}
}
else
{
dp[i][j] = 0;
}
}
}
cout << "max len is " << max_len << endl;
cout << "star index is" << start_index << endl;
return max_len;
}