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chunked-palindrome
Normal palindrome is defined as a string that reads the same backwards as forwards, for example "abccba".
Chunked palindrome is defined as a string that you can split into chunks and it will form a palindrome.
For example, "volvo". You can split it into (vo)(l)(vo). Let A = "vo", B = "l", so the original string is ABA which is a palindrome.
Given a string str, find the maximum number of chunks we can split that string to get a chuncked palindrome.
Example 1:
Input: "valve"
Output: 1
Explanation: You can't split it into multiple chunks so just return 1 (valve)
Example 2:
Input: "voabcvo"
Output: 3
Explanation: (vo)(abc)(vo)
Example 3:
Input: "vovo"
Output: 2
Explanation: (vo)(vo)
Example 4:
Input: "volvolvo"
Output: 5
Explanation: (vo)(l)(vo)(l)(vo)
Example 5:
Input: "volvol"
Output: 2
Explanation: (vol)(vol)
Example 6:
Input: "aaaaaa"
Output: 6
Explanation: We can split it into (aaa)(aaa), but the optimal split should be (a)(a)(a)(a)(a)(a)
Questions from the same interview:
Product of K consecutive numbers
给定一个字符串，让求出最多可以切成分块的回文，每一个切分可以是一个子字符串，或者单个字符。
例如，
"aaaaaa"， 可以切分成 "aaa)(aaa)" - 2， 但是这里要求最多分块， 这样就是最多的"(a)(a)(a)(a)(a)(a)" - 6分析， 满足回文字符串的要求是，从前读和从后读是一样的， 例如，
"aba"， "anna"，"madam" 等那么这里就可以分别从前
（l）和从后（r）扫描，l 和 r 记录前后扫描的index， 然后用pre_l and pre_r 记录前一次扫描到的可以分块的回文位置，如果子字符串相同（substr（pre_l, l + 1) 这里包含边界），结果 +2，继续扫描。
如果最后剩余一个（奇数个chunk）， 那么直接结果 +1， 否则偶数个chunk， 直接返回结果
例如：
"volvolvo"
alt text
时间复杂度：
O(N^2) - N is the s length, s.substring()时间复杂度是O(n)空间复杂度：
O(1) - 没有额外的空间从解法一中我们可以看到
palindome 左右对称， 所以可以从左和右，用递归求解。如下图例子， 可以从左起子字符串匹配最右起的子字符串。绿色框框，如果匹配， 递归的计算最长的回文，即每次碰到回文就计算 +2， 直到最后字符串中没有匹配的回文，或者是匹配到最后， 退出， 返回结果。
例如：
"volvolvo"
alt text
解法一
class ChunkedPalindrom {
public static int maxChunkedPalindrome2(String s) {
if (s == null || s.length() == 0) return 0;
int l = 0;
int r = s.length() - 1;
int max = 0;
int preL = l;
int preR = r;
while (l < r) {
String prefix = s.substring(preL, l + 1); // include right
String sufix = s.substring(r, preR + 1);
if (prefix.equals(sufix)) {
preL = l + 1;
preR = r - 1;
max += 2;
}
l++;
r--;
}
if (preL <= preR) max++;
System.out.println("max chunk palindrom: " + max);
return max;
}
}
解法二
class ChunkedPalindrome {
public static int maxChunkedPalindrome(String s) {
if (s == null || s.length() == 0) return 0;
return helper(s, 0, 0, s);
}
private static int helper(String curr, int count, int len, String s) {
// no substring left, return current count
if (curr == null || curr.isEmpty()) return count;
if (curr.length() <= 1) {
if (count != 0 && s.length() - len <= 1) {
return count + 1;
} else return 1;
}
int currLen = curr.length();
// get left and right substring and compare
for (int i = 0; i < currLen / 2; i++) {
String left = curr.substring(0, i + 1);
String right = curr.substring(currLen - 1 - i, currLen);
if (left.equals(right)) {
// if left and right match, then continue match the rest substring (s - left - right)
return helper(curr.substring(i + 1, currLen - 1 - i),
count + 2, len + (i + 1) * 2, s);
}
}
return count + 1;
}
}
Last modified 4yr ago