20200326
繼續刷題
題目 :Z字形變換
將一個給定字符串根據給定的行數,以從上往下,從左往右進行Z字形排列。
比如輸入字符串爲"LEETCODEISHIRING"
行數爲 3 時,排列如下:
L C I R
E T O E S I I G
E D H N
之後,你的輸出需要從左往右逐行讀取,產生一個新的字符串,比如:"LCIRETOESIIGEDHN"
。
示例:
輸入: s = "LEETCODEISHIRING", numRows = 3
輸出: "LCIRETOESIIGEDHN"
code1
class Solution {
public String convert(String s, int numRows) {
if(s==null || numRows<=1){
return s;
}
int n = s.length();
//取numRows,字符串s長度的較小值,用這個較小值來創建n個StringBuilder
int rows = Math.min(n,numRows);
StringBuilder[] arr = new StringBuilder[rows];
for(int i=0;i<arr.length;++i){
arr[i] = new StringBuilder();
}
int j=0;
//向上還是向下的標誌位
boolean isDown = false;
StringBuilder res = arr[0];
//遍歷字符串s,並將字符放到arr[j]中,之後根據標誌位來判斷往下還是往上
for(int i=0;i<n;++i){
arr[j].append(s.charAt(i));
if(j==0 || j==numRows-1){
isDown = !isDown;
}
if(isDown){
++j;
}else{
--j
}
}
for(int i=1;i<arr.length;++i){
res.append(arr[i]);
}
return res.toString();
}
}
code2
class Solution {
public String convert(String s, int numRows) {
if (numRows == 1) return s;
List<StringBuilder> rows = new ArrayList<>();
for (int i = 0; i < Math.min(numRows, s.length()); i++)
rows.add(new StringBuilder());
int curRow = 0;
boolean goingDown = false;
for (char c : s.toCharArray()) {
rows.get(curRow).append(c);
if (curRow == 0 || curRow == numRows - 1) goingDown = !goingDown;
curRow += goingDown ? 1 : -1;
}
StringBuilder ret = new StringBuilder();
for (StringBuilder row : rows) ret.append(row);
return ret.toString();
}
}