leetcode 6. ZigZag Conversion

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 text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

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题意挺难懂吧。就是把字符串Z型实现，而且不是ZZ这样，就是纵项和斜项交叉显示。

刚开始打算直接用string实现，然后寻找下标的关系，但是发现有可能有多个Z

后来发现我们只需要逐个打印每行，这样用map实现不是很好嘛~！

所以计算下标的规律就好了。

class Solution {
public:

    string convert(string s, int numRows) {
        string result="";
        int len=s.length();
        if(numRows>=len||numRows==1) return s;
        int c=numRows-2;     //斜项的个数
        int g=c+numRows;     //一个z需要的个数（因为不是ZZ而是纵项斜项交叉的，所以不是2*numRows+c）
        int index=0;
        map<int,string> mp;
        for(int i=0;i<len;i++){
            index=i%g;
            if(0<=index&&index<=numRows-1) mp[index]+=s[i];
            if(numRows<=index&&index<=numRows+c-1) mp[numRows+c-index]+=s[i];
        }
        for(auto i=mp.begin();i!=mp.end();i++){
            result+=(*i).second;       
        }
        return result;
    }
};