Subject: https://leetcode-cn.com/problems/zigzag-conversion/
Answer: Find the pattern
public String convert(String s, int numRows) {
if(numRows < 2) return s;
List<StringBuilder> list = new ArrayList<>();
for(int i=0;i<numRows;i++) list.add(new StringBuilder());
int i=0;
int tag = -1;
for(char c:s.toCharArray()){
list.get(i).append(c);
if(i==0 || i==numRows-1) tag = -tag;
i=i+tag;
}
StringBuilder result = new StringBuilder();
for(StringBuilder stringBuilder:list){
result.append(stringBuilder);
}
return result.toString();
}