The String ZigZag Conversion Algorithms

  • 时间：2020-09-12 10:17:13
  • 分类：网络文摘
  • 阅读：126 次

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 s, int numRows);
Example 1:

Input: s = “PAYPALISHIRING”, numRows = 3
Output: “PAHNAPLSIIGYIR”
Example 2:

Input: s = “PAYPALISHIRING”, numRows = 4
Output: “PINALSIGYAHRPI”
Explanation:

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

The String ZigZag Conversion Algorithms

We can simulate the process by walking down first, then when it reaches the last row, bounces back in the reverse direction. We need arrays of strings as we walk, and append the characters to the corresponding row of string.

O(N) time and O(N) space requirement. Edge case is when the ZigZag row is one and then we have to return the original string.

C++ String ZigZag Conversion
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

class Solution {
public:
    string convert(string s, int numRows) {
        if (numRows == 1) return s;
        vector<string> rows(min((int)s.size(), numRows));
        bool down = false;        
        int row = 0;
        for (int i = 0; i < s.size(); ++ i) {
            rows[row] += s[i];
            if ((row == 0) || (row == numRows - 1)) {
                down = !down;
            }
            row += down ? 1 : -1;
        }        
        string ss = "";
        for (const auto &n: rows) {
            ss += n;
        }
        return ss;
    }
};
class Solution {
public:
    string convert(string s, int numRows) {
        if (numRows == 1) return s;
        vector<string> rows(min((int)s.size(), numRows));
        bool down = false;        
        int row = 0;
        for (int i = 0; i < s.size(); ++ i) {
            rows[row] += s[i];
            if ((row == 0) || (row == numRows - 1)) {
                down = !down;
            }
            row += down ? 1 : -1;
        }        
        string ss = "";
        for (const auto &n: rows) {
            ss += n;
        }
        return ss;
    }
};
Python String ZigZag Conversion
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows == 1:
            return s
        data = [''] * numRows
        down = False
        row = 0
        for i in s:
            data[row] += i
            if row == 0 or row == numRows - 1:
                down = not down
            row = row + 1 if down else row - 1
        x = ''
        for j in data:
            if j != '':
                x = x + j
        return x
class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows == 1:
            return s
        data = [''] * numRows
        down = False
        row = 0
        for i in s:
            data[row] += i
            if row == 0 or row == numRows - 1:
                down = not down
            row = row + 1 if down else row - 1
        x = ''
        for j in data:
            if j != '':
                x = x + j
        return x
Javascript String ZigZag Conversion
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27

/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {
    if (numRows === 1) return s;
    let data = [];
    let row = 0;
    let down = false;
    for (let x of s) {
        if (typeof data[row] === 'undefined') {
            data[row] = x;
        } else {
            data[row] += x;
        }
        if (row === 0 || row === numRows - 1) {
            down = !down;
        }
        row += down ? 1 : -1;
    }
    let res = '';
    for (let i = 0; i < Math.min(numRows, s.length); ++ i) {
        res += data[i];
    }
    return res;
};
/**
 * @param {string} s
 * @param {number} numRows
 * @return {string}
 */
var convert = function(s, numRows) {
    if (numRows === 1) return s;
    let data = [];
    let row = 0;
    let down = false;
    for (let x of s) {
        if (typeof data[row] === 'undefined') {
            data[row] = x;
        } else {
            data[row] += x;
        }
        if (row === 0 || row === numRows - 1) {
            down = !down;
        }
        row += down ? 1 : -1;
    }
    let res = '';
    for (let i = 0; i < Math.min(numRows, s.length); ++ i) {
        res += data[i];
    }
    return res;
};

–EOF (The Ultimate Computing & Technology Blog) —

推荐阅读：
8 Things To Include In Your Blog Privacy Policy　 Customer Success Strategy: 7 Reasons Why You Need One for Your B　 Tips On Creating Content For Marketing For 2020　 Best Image Optimizer Plugins for WordPress in 2019　 A Blogger’s Guide to Successful Content Marketing in a Saturated　 6 Remote Jobs For Supplemental Income　 5 Tips When Preparing for a Business Conference　 Customizing WordPress with Branda by WPMU DEV　 How to Blog Like Shakespeare　 Depth First Search Algorithm to Delete Insufficient Nodes in Roo　
评论列表
添加评论