[Leetcode] ZigZag Conversion

时间：2014-04-27 21:36:45 收藏：0 阅读：515

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".

注意如果用push_back的话会超内存，因为每次push_back后如果空间不够则新空间会是原来的两倍，为了避免这种情况还是直接定义长度为len的字符串吧。题目根本就没说清楚嘛，下面是n=4时的结果：

P     I     N
A   L S   I G
Y A   H R
P     I

 1 class Solution {
 2 public:
 3     string convert(string s, int nRows) {
 4         int len = s.length();
 5         if (len <= nRows || nRows == 1) return s;
 6         int steps;
 7         string res;
 8         res.resize(len);
 9         int idx = 0;
10         for (int i = 0; i < nRows; ++i) {
11             if (i == nRows - 1) steps = 2 * (nRows - 1);
12             else steps = 2 * (nRows - i - 1);
13             
14             if (i == 0 || i == nRows - 1) {
15                 for (int j = i; j < len; j += steps) {
16                     res[idx] = s[j];
17                     ++idx;
18                 }
19             } else {
20                 bool flag = true;
21                 for (int j = i; j < len;) {
22                     res[idx] = s[j];
23                     ++idx;
24                     if (flag) j += steps;
25                     else j += (2 * (nRows - 1) - steps);
26                     flag = !flag;
27                 }
28             }
29         }
30         return res;
31     }
32 };

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