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 RAnd 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"
.題目的意思就是把一個string從頭到尾按下面的方式排放(以四行爲例):
然後再以{‘1’‘7’‘13’} {‘2’‘6’‘8‘’12‘} {’3‘’5‘’9‘’11‘} {’4‘’10‘},給定的行數已經在傳遞參數的時候確定了,我們要分開處理每一行;
注意看兩個縱列{1,2,3,4}和{7,8,9,10},相差剛好爲 2 * nRows - 2;
(而除了第一行和最後一行,其他行中間還隔着一個字符,而這個與字符的位置剛好相差 (nRows - i - 1) * 2 , i 是當前行<0開始>)
再加入越界的判斷,我們可以得到下面算法:
class Solution {
public:
string convert(string s, int nRows)
{
if( nRows <= 1 )
{
return s;
}
string ret{};
int len = s.length();
int add = 2 * nRows - 2;
for( int i = 0; i < nRows; i++ )
{
for(int j = i; j < len; j+=add)
{
ret += s[j];
if (i != 0 && i != nRows - 1 && j + (nRows-i-1) * 2 < s.length())
{
ret += s[j + (nRows-i-1) * 2];
}
}
}
return ret;
}
};