1、
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"
.
分析:之字形扫描,有一个特点,如下图所示,每一层的下一个坐标和上一个坐标有递推关系,并设置一个标志是先往下再往上还是先向下再往上。
代码如下:
class Solution {
public:
string convert(string s, int nRows) {
string result;
if(s.length()<1 || nRows <= 0){
return result;
}else if(nRows == 1){
return s;
}
result = s;
bool isDownUp = true;
for(int i=0,j=0,k=0; i<nRows && j<s.length();++j){
result[j] = s[k];
if(i == 0 || i == nRows-1){
k += (nRows-1)*2;
}else{
if(isDownUp){
k += (nRows-i-1)*2;
isDownUp = false;
}else{
k += i*2;
isDownUp = true;
}
}
if(k > s.length()-1){ //层数加1
++i;
k = i;
isDownUp = true;
}
}
return result;
}
};