LeetCode--zigzag-conversion

题目描述

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 text, int nRows);

convert("PAYPALISHIRING", 3)should return"PAHNAPLSIIGYIR".
分析：用一个vector存储每一行的string，用一个变量step确定行号的行走方向，到达第一行时向下，到达最后一行时向上，最后将得到的string按照行号依次连接。

class Solution {
public:
    string convert(string s, int nRows) {
        if(nRows <= 1)
            return s;
        vector<string> z(nRows,"");
        int step = 1,row = 0;
        int l = s.size();
        for(int i=0;i<l;i++)
        {
            z[row] += s[i];
            if(row == 0)
                step = 1;
            else if(row == nRows-1)
                step = -1;
            row += step;
        }
        string result = "";
        for(int i=0;i<nRows;i++)
            result += z[i];
        return result;
    }
};