diff --git a/problems/0131.分割回文串.md b/problems/0131.分割回文串.md index 822d4399..4a868651 100644 --- a/problems/0131.分割回文串.md +++ b/problems/0131.分割回文串.md @@ -310,39 +310,35 @@ public: ### Java ```Java class Solution { - List> lists = new ArrayList<>(); - Deque deque = new LinkedList<>(); - + //保持前几题一贯的格式, initialization + List> res = new ArrayList<>(); + List cur = new ArrayList<>(); public List> partition(String s) { - backTracking(s, 0); - return lists; + backtracking(s, 0, new StringBuilder()); + return res; } - - private void backTracking(String s, int startIndex) { - //如果起始位置大于s的大小,说明找到了一组分割方案 - if (startIndex >= s.length()) { - lists.add(new ArrayList(deque)); + private void backtracking(String s, int start, StringBuilder sb){ + //因为是起始位置一个一个加的,所以结束时start一定等于s.length,因为进入backtracking时一定末尾也是回文,所以cur是满足条件的 + if (start == s.length()){ + //注意创建一个新的copy + res.add(new ArrayList<>(cur)); return; } - for (int i = startIndex; i < s.length(); i++) { - //如果是回文子串,则记录 - if (isPalindrome(s, startIndex, i)) { - String str = s.substring(startIndex, i + 1); - deque.addLast(str); - } else { - continue; + //像前两题一样从前往后搜索,如果发现回文,进入backtracking,起始位置后移一位,循环结束照例移除cur的末位 + for (int i = start; i < s.length(); i++){ + sb.append(s.charAt(i)); + if (check(sb)){ + cur.add(sb.toString()); + backtracking(s, i + 1, new StringBuilder()); + cur.remove(cur.size() -1 ); } - //起始位置后移,保证不重复 - backTracking(s, i + 1); - deque.removeLast(); } } - //判断是否是回文串 - private boolean isPalindrome(String s, int startIndex, int end) { - for (int i = startIndex, j = end; i < j; i++, j--) { - if (s.charAt(i) != s.charAt(j)) { - return false; - } + + //helper method, 检查是否是回文 + private boolean check(StringBuilder sb){ + for (int i = 0; i < sb.length()/ 2; i++){ + if (sb.charAt(i) != sb.charAt(sb.length() - 1 - i)){return false;} } return true; }