[LeetCode] 131. Palindrome Partitioning 回文分割

2021年09月15日 阅读数:1
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Given a string s, partition s such that every substring of the partition is a palindrome.html

Return all possible palindrome partitioning of s.java

Example:python

Input: "aab"
Output:
[
  ["aa","b"],
  ["a","a","b"]
]

解法1:dfs, 回溯Backchecking,app

解法2:DPpost

Java:url

public class Solution {
        List<List<String>> resultLst;
	    ArrayList<String> currLst;
	    public List<List<String>> partition(String s) {
	        resultLst = new ArrayList<List<String>>();
	        currLst = new ArrayList<String>();
	        backTrack(s,0);
	        return resultLst;
	    }
	    public void backTrack(String s, int l){
	        if(currLst.size()>0 //the initial str could be palindrome
	            && l>=s.length()){
	                List<String> r = (ArrayList<String>) currLst.clone();
	                resultLst.add(r);
	        }
	        for(int i=l;i<s.length();i++){
	            if(isPalindrome(s,l,i)){
	                if(l==i)
	                    currLst.add(Character.toString(s.charAt(i)));
	                else
	                    currLst.add(s.substring(l,i+1));
	                backTrack(s,i+1);
	                currLst.remove(currLst.size()-1);
	            }
	        }
	    }
	    public boolean isPalindrome(String str, int l, int r){
	        if(l==r) return true;
	        while(l<r){
	            if(str.charAt(l)!=str.charAt(r)) return false;
	            l++;r--;
	        }
	        return true;
	    }
}

Java: DPrest

public class Solution {
 	public static List<List<String>> partition(String s) {
		int len = s.length();
		List<List<String>>[] result = new List[len + 1];
		result[0] = new ArrayList<List<String>>();
		result[0].add(new ArrayList<String>());

		boolean[][] pair = new boolean[len][len];
		for (int i = 0; i < s.length(); i++) {
			result[i + 1] = new ArrayList<List<String>>();
			for (int left = 0; left <= i; left++) {
				if (s.charAt(left) == s.charAt(i) && (i-left <= 1 || pair[left + 1][i - 1])) {
					pair[left][i] = true;
					String str = s.substring(left, i + 1);
					for (List<String> r : result[left]) {
						List<String> ri = new ArrayList<String>(r);
						ri.add(str);
						result[i + 1].add(ri);
					}
				}
			}
		}
		return result[len];
	}
}  

Python:htm

# Time:  O(2^n)
# Space: O(n)
# recursive solution
class Solution:
    # @param s, a string
    # @return a list of lists of string
    def partition(self, s):
        result = []
        self.partitionRecu(result, [], s, 0)
        return result

    def partitionRecu(self, result, cur, s, i):
        if i == len(s):
            result.append(list(cur))
        else:
            for j in xrange(i, len(s)):
                if self.isPalindrome(s[i: j + 1]):
                    cur.append(s[i: j + 1])
                    self.partitionRecu(result, cur, s, j + 1)
                    cur.pop()

    def isPalindrome(self, s):
        for i in xrange(len(s) / 2):
            if s[i] != s[-(i + 1)]:
                return False
        return True

Python:blog

# Time:  O(n^2 ~ 2^n)
# Space: O(n^2)
# dynamic programming solution
class Solution:
    # @param s, a string
    # @return a list of lists of string
    def partition(self, s):
        n = len(s)

        is_palindrome = [[0 for j in xrange(n)] for i in xrange(n)]
        for i in reversed(xrange(0, n)):
            for j in xrange(i, n):
                is_palindrome[i][j] = s[i] == s[j] and ((j - i < 2 ) or is_palindrome[i + 1][j - 1])

        sub_partition = [[] for i in xrange(n)]
        for i in reversed(xrange(n)):
            for j in xrange(i, n):
                if is_palindrome[i][j]:
                    if j + 1 < n:
                        for p in sub_partition[j + 1]:
                            sub_partition[i].append([s[i:j + 1]] + p)
                    else:
                        sub_partition[i].append([s[i:j + 1]])

        return sub_partition[0]

Python: worem

class Solution(object):
    def partition(self, s):
        """
        :type s: str
        :rtype: List[List[str]]
        """
        res = []
        self.helper(res, s, [], 0)
        
        return res
        
    def helper(self, res, s, cur, l):
        if l == len(s):
            res.append(list(cur))
            return
            
        for r in range(l, len(s)):
            if self.isPalindrome(s, l, r):
                if l == r:
                    cur.append(s[l])
                else:
                    cur.append(s[l:r+1])
                self.helper(res, s, cur, r + 1)
                cur.pop()     
        
    def isPalindrome(self, s, l, r):
        while l < r:
            if s[l] != s[r]:
                return False
            l += 1
            r -= 1
        return True 

Python:

class Solution(object):
    def partition(self, s):
        """
        :type s: str
        :rtype: List[List[str]]
        """
        res = []
        self.dfs(s, [], res)
        return res

    def dfs(self, s, path, res):
        if not s:
            res.append(path)
            return
        for i in range(1, len(s)+1):
            if self.isPal(s[:i]):
                self.dfs(s[i:], path+[s[:i]], res)

    def isPal(self, s):
        return s == s[::-1]
            res = []
            self.helper(res, s, [], 0)

            return res

Python:

class Solution(object):
    def partition(self, s):
        """
        :type s: str
        :rtype: List[List[str]]
        """
        return [[s[:i]] + rest
                for i in xrange(1, len(s)+1)
                if s[:i] == s[i-1::-1]
                for rest in self.partition(s[i:])] or [[]] 

C++:

class Solution {
public:
    vector<vector<string>> partition(string s) {
        vector<vector<string>> res;
        vector<string> out;
        partitionDFS(s, 0, out, res);
        return res;
    }
    void partitionDFS(string s, int start, vector<string> &out, vector<vector<string>> &res) {
        if (start == s.size()) {
            res.push_back(out);
            return;
        }
        for (int i = start; i < s.size(); ++i) {
            if (isPalindrome(s, start, i)) {
                out.push_back(s.substr(start, i - start + 1));
                partitionDFS(s, i + 1, out, res);
                out.pop_back();
            }
        }
    }
    bool isPalindrome(string s, int start, int end) {
        while (start < end) {
            if (s[start] != s[end]) return false;
            ++start;
            --end;
        }
        return true;
    }
};

  

 

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