Title Description

Will a given string s According to the given number of rows numRows , From top to bottom 、 Left to right Z Font arrangement .（ There's a problem with the person who wrote the question , Obviously И Font conversion , I have to say Z）
For example, the input string is “PAYPALISHIRING” The number of rows is 3 when , Arranged as follows ：

P   A   H   N
A P L S I I G
Y   I   R

after , The output needs to be read line by line from left to right , Generate a new string , such as ：“PAHNAPLSIIGYIR”.
Please implement this function to transform a string into a specified number of lines ：

string convert(string s, int numRows);

Example 1

 Input ：s = "PAYPALISHIRING", numRows = 3
 Output ："PAHNAPLSIIGYIR"

Example 2

 Input ：s = "PAYPALISHIRING", numRows = 4
 Output ："PINALSIGYAHRPI"
 explain ：
P     I    N
A   L S  I G
Y A   H R
P     I

Example 3

 Input ：s = "A", numRows = 1
 Output ："A"

Ideas

1       9        17
2     8 10     16 .
3   7   11   15   .
4 6     12 14     .
5       13        . . 

In fact, the string is processed in the above way S Arrange , Then line by line is spliced together to form a new string and return .

string convert(string s, int numRows) {
    
	string ans;
	if(numRows==1)
		return s;
	vector<string> a(numRows);
	int i=0;
	int flag=0;// Used to interpret the traversal order of the current line  0： From top to bottom  1： From bottom to top 
	for(int  k=0;k<s.length();k++){
    
		if( flag==0 && i<numRows-1 ){
    // From top to bottom   Did not reach the border 
			a[i].push_back(s[k]);
			i++;
		}
		else if(flag==0 && i==numRows-1){
    // From top to bottom   Reach the border 
			a[i].push_back(s[k]);
			flag=1;
			i--;
		}
		else if( flag==1 && i>0 ){
    // From bottom to top   Did not reach the border 
			a[i].push_back(s[k]);
			i--;
		}
		else if(flag==1 && i==0){
    // From bottom to top   Reach the border 
			a[i].push_back(s[k]);
			flag=0;
			i++;
		}
	}
	
	for(int ii=0;ii<numRows;ii++)
		ans+=a[ii];
		
	return ans;
}

The title is not difficult. , Mainly thinking , It also tests the structure and operation of data .