6. ZigZag Conversion

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".

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {
    var resArr = [];
    var len = s.length;
    
    var index = 1;
    
    //1行的或者直接就是空的，直接就输出了
    if(numRows === 1 || !s){
        return s;
    }
    
    //初始化
    for(var i = 0;i < numRows;i++){
        resArr[i] = '';
    }
    
    //一直上下循环添加
    for(var i = 0;i<len;i++){
        
        if(index == 1){
            
             sub = 1;
        }
        
        if(index == numRows){
            sub = -1;
        }
        
        resArr[index - 1] += s[i];
        index += sub;
        
    }
    
    return resArr.join("");
    
};