笔试练习四

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第一题:最长回文子序列

题目思想大概是这样:cabbeaf:回文子序列有:c,a,aa,bb,,aba,abba,e,f,最长的就是abba,所以输出长度为4

#include <iostream>#include <algorithm>#include <string>int dp[1000][1000];using namespace std;int main(){//思路就是求这个原字符串和它反转字符串的最长公共子序列  string str;  cin>>str;  string a=str;  reverse(a.begin(),a.end());  int len=str.length();  for(int i=1;i<=len;i++){    for(int j=1;j<=len;j++){      if(str[i-1]==a[j-1]){        dp[i][j]=dp[i-1][j-1]+1;      }      else{        dp[i][j]=max(dp[i-1][j],dp[i][j-1]);      }    }  }    cout<<dp[len][len];  return 0;}

第二题蛇形矩阵:

题目大意是这样:

输入2

矩阵为

1 2

4 3

输出:1 2 4 3//按行打印

输入3

矩阵为

1 2 3

8 9 4

7 6 5

输出:1 2 3 8 9 4 7 6 5 //按行打印

#include<iostream>#include<vector>using namespace std;void Fun(const int n){  vector<int > elem;  elem.resize(n);  vector<vector<int > >array(n,elem);  int topLeft[2]={0,0};  int topRigth[2] = {0,n-1};  int bottomRight[2]={n-1,n-1};  int bottomLeft[2]={n-1,0};  int row=0,col =0;  int counter = 0;  int i=0,j=0;  while(true)  {    row = topLeft[0];    col = topLeft[1];    while(col<=topRigth[1])    {      array[row][col++] = ++counter;    }    topRigth[0]+=1;    topRigth[1]-=1;        row=topRigth[0];    col = topRigth[1]+1;    while(row<=bottomRight[0])    {      array[row++][col] = ++counter;    }        bottomRight[0] -=1;    bottomRight[1]-=1;        row = bottomRight[0]+1;    col=bottomRight[1];    while(col>=bottomLeft[1])    {      array[row][col--]-=++counter;    }        bottomLeft[0]-=1;    bottomLeft[1]+=1;        row = bottomLeft[0];    col = bottomLeft[1]-1;    while(row>topLeft[0])    {      array[row--][col]=++counter;    }        topLeft[0]+=1;    topLeft[1]+=1;    if(topLeft[1]>=topRigth[1])    {      if(0!=n%2)      {        array[n/2][n/2]=++counter;      }      break;    }  }    for(i=0;i<n;i++)  {    for(j=0;j<n;j++)    {     if(array[i][j]<0)     {       array[i][j]*=-1;     }      cout<<array[i][j]<<" ";    }  }  cout<<endl;}int main(){  int n = 0;  cin>>n;  Fun(n);  return 0;}

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