【LeetCode】ZigZag Conversion

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題目

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   NA P L S I I GY   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".

解答

數學問題，先找好規律，然後按順序直接在原字串上讀取下標擷取。

nRow = 2:0 2 4 6 8 10 121 3 5 7 9 11 13nRow = 3: 0     4      8     12 1  3  5   7  9  112     6     10nRow = 4:0      6       121   5  7    11 132 4    8  103      9

顯然，首行和末行的字元間隔是2*nRows-2，之後的字元間隔逐行減2……代碼如下：

public class Solution {    public String convert(String s, int nRows) {        if(nRows==1)            return s;        int dis=2*nRows-2;  //首行(末行)的相鄰字母的間隔        int len=s.length();        String result="";        for(int i=0;i<nRows;i++){            for(int j=i;j<len;j+=dis){                result+=s.charAt(j);                if(i>0&&i<nRows-1&&j+dis-2*i<len)  //處理不是首行和末行的                    result+=s.charAt(j+dis-2*i);            }        }        return result;    }}

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