[LeetCode-Java]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”.

解：时间复杂度 O(n)

public String convert(String s, int numRows) {

StringBuilder stringBuilder = new StringBuilder();

if (numRows <= 1){
stringBuilder.append(s);
}else {
int gap = 2 * (numRows - 1);
//第一行
for (int i = 0; i < s.length(); i += gap) {
stringBuilder.append(s.charAt(i));
}

//中间行
for (int n = 1; n < numRows-1; n++) {

for (int i = 0; i - n < s.length(); i += gap) {
if (i-n>0) {
stringBuilder.append(s.charAt(i - n));
}
if (i+n<s.length()){
stringBuilder.append(s.charAt(i + n));
}
}
}

//最后一行
for (int i = numRows-1; i < s.length(); i += gap) {
stringBuilder.append(s.charAt(i));
}
}

return stringBuilder.toString();
}