将一个给定字符串根据给定的行数,以从上往下、从左到右进行 Z 字形排列。
比如输入字符串为 "LEETCODEISHIRING"
行数为 3 时,排列如下:
L C I R
E T O E S I I G
E D H N
之后,你的输出需要从左往右逐行读取,产生出一个新的字符串,比如:"LCIRETOESIIGEDHN"
。
请你实现这个将字符串进行指定行数变换的函数:
string convert(string s, int numRows);
输入: s = "LEETCODEISHIRING", numRows = 3
输出: "LCIRETOESIIGEDHN"
输入: s = "LEETCODEISHIRING", numRows = 4
输出: "LDREOEIIECIHNTSG"
解释:
L D R
E O E I I
E C I H N
T S G
class Solution {
public:
string convert(string s, int numRows) {
if (numRows == 1) return s;
vector<string> strings(numRows);
auto p = s.begin();
bool forward = true;
int i = 0;
while(p<s.end()){
if(forward){
strings[i].push_back(*p);
++p;
if(i!=numRows-1) ++i;
else{
forward = false;
--i;
}
}else{
strings[i].push_back(*p);
++p;
if(i!=0) --i;
else{
forward = true;
++i;
}
}
}
string res;
for(string str:strings) res.append(str);
return res;
}
};
代码优化:
class Solution {
public:
string convert(string s, int numRows) {
if (numRows == 1) return s;
vector<string> rows(min(numRows, int(s.size())));
int curRow = 0;
bool goingDown = false;
for (char c : s) {
rows[curRow] += c;
if (curRow == 0 || curRow == numRows - 1) goingDown = !goingDown;
curRow += goingDown ? 1 : -1;
}
string ret;
for (string row : rows) ret += row;
return ret;
}
};