Zigzag Conversion
23 Nov 2019#ZigZag Conversion
Intro
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
Idea
The description of the problem is misleading. This is just a way to output the string s;
And the rule is, give you a number n(NumRows), you start to scan the string. When i < n, keep i increasing, and when i reached n, then keep i decreasing.
| Line |
| 0 | a | g |
| 1 | b | f | h |
| 2 | c | e | i |
| 3 | d | j |
Code
public String convert(String s, int numRows) {
int index = 0;
StringBuilder[] sb = new StringBuilder[numRows];
for(int i=0; i<numRows; i++) {
sb[i] = new StringBuilder();
}
while(index < s.length()) {
// first increse i from 0 -> n-1;
for(int i=0; i<numRows && index < s.length(); i++) {
sb[i].append(s.charAt(index));
index++;
}
// then decrease i fron n-2 -> 1;
for(int i=numRows-2; i>0 && index < s.length(); i--) {
sb[i].append(s.charAt(index));
index++;
}
}
StringBuilder ans = new StringBuilder();
for(StringBuilder ss : sb) {
ans.append(ss);
}
return ans.toString();
}