LeetCode第六题——zigzag conversion

问题描述
The string “PAYPALISHIRING” is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P A H N
A P L S I I G
Y I R
And then read line by line: “PAHNAPLSIIGYIR”

Write the code that will take a string and make this conversion given a number of rows:

string convert(string s, int numRows);
Example 1:

Input: s = “PAYPALISHIRING”, numRows = 3
Output: “PAHNAPLSIIGYIR”
Example 2:

Input: s = “PAYPALISHIRING”, numRows = 4
Output: “PINALSIGYAHRPI”
Explanation:

P I N
A L S I G
Y A H R
P I
解法思路
这个问题的关键在于理解zigzag是怎么排列字符的，上网查了相关信息才知道，类似于“|/|"这种N镜像的排列数字。掌握这个之后就容易多了，建立一个二维字符数组，依照顺序将各个字符加入进去，值得注意的是：对于同一行，可不添加空字符（示例里面有空字符）。
C++代码

class Solution {
public:
    string convert(string s, int numRows) {
        int n=s.size();
        vector<vector<char>> str;
        str.resize(numRows);
        int j=0;
       int i=0;
        int flag=0;
       while(i<n)
       {
           if(flag==1)
           {
               for(int a=numRows-2;a>=1;--a)
               {
                   str[a].push_back(s[i]);
                   ++i;
                   if(i>=n) break;
               }
               flag=0;
           }
           else
           {
               str[j].push_back(s[i]);
               ++i;
               if(j==numRows-1)
               {
                   flag=1;
               }
               ++j;
               j=j%numRows;
           }
       }
        string s1;
        for(int a=0;a<str.size();++a)
        {
            for(int b=0;b<str[a].size();++b)
            {
                s1+=str[a][b];
            }
        }
        return s1;
       
    }
};

**结果分析”
Runtime: 76 ms, faster than 13.08% of C++ online submissions for ZigZag Conversion.
Memory Usage: 22.7 MB, less than 18.63% of C++ online submissions for ZigZag Conversion.
算法效率很差，需要进一步改进！

LeetCode第六题——zigzag conversion

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