ZigZag Conversion
描述
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
要找到数学规律。真正面试中,不大可能出这种问题。
n=4:
P I N
A L S I G
Y A H R
P I
n=5:
P H
A S I
Y I R
P L I G
A N
所以,对于每一层垂直元素的坐标 (i,j)= (j+1 )*n +i
;对于每两层垂直元素之间的插入元素(斜对角元素),(i,j)= (j+1)*n -i
代码
// LeetCode, ZigZag Conversion
// 时间复杂度O(n),空间复杂度O(1)
class Solution {
public:
string convert(string s, int nRows) {
if (nRows <= 1 || s.size() <= 1) return s;
string result;
for (int i = 0; i < nRows; i++) {
for (int j = 0, index = i; index < s.size();
j++, index = (2 * nRows - 2) * j + i) {
result.append(1, s[index]); // 垂直元素
if (i == 0 || i == nRows - 1) continue; // 斜对角元素
if (index + (nRows - i - 1) * 2 < s.size())
result.append(1, s[index + (nRows - i - 1) * 2]);
}
}
return result;
}
};