题目

法1：DFS+双指针

必须掌握基础方法！
注意：使用ArrayList删除尾元素比LinkedList要快很多！！！

class Solution {
    public List<List<String>> partition(String s) {
        List<List<String>> res = new ArrayList<>();
        if (s.length() == 0) {
            return res;
        }
        List<String> tmp = new ArrayList<>();
        dfs(s, 0, tmp, res);

        return res;
    }

    public void dfs(String s, int startIndex, List<String> tmp, List<List<String>> res) {
        if (startIndex == s.length()) {
            res.add(new ArrayList<>(tmp));
            return;
        }
        for (int i = startIndex; i < s.length(); ++i) {
            if (!valid(s, startIndex, i)) {
                continue;
            }
            tmp.add(s.substring(startIndex, i + 1));
            dfs(s, i + 1, tmp, res);
            tmp.remove(tmp.size() - 1);
        }
    }

    public boolean valid(String s, int startIndex, int endIndex) {
        while (startIndex <= endIndex) {
            char left = s.charAt(startIndex);
            char right = s.charAt(endIndex);
            if (left != right) {
                return false;
            }
            ++startIndex;
            --endIndex;
        }

        return true;
    }
}

法2：DFS+回文串判断预处理

主要优化回文串判断部分

class Solution {
    public List<List<String>> partition(String s) {
        List<List<String>> res = new ArrayList<>();
        int n = s.length();
        if (n == 0) {
            return res;
        }
        boolean[][] valid = new boolean[n][n];
        List<String> tmp = new ArrayList<>();
        for (int i = 0; i < n; ++i) {
            Arrays.fill(valid[i], true);
        }
        for (int i = n - 1; i >= 0; --i) {
            for (int j = i + 1; j < n; ++j) {
                valid[i][j] = (s.charAt(i) == s.charAt(j)) && valid[i + 1][j - 1];
            }
        }
        dfs(s, 0, tmp, res, valid);

        return res;
    }

    public void dfs(String s, int startIndex, List<String> tmp, List<List<String>> res, boolean[][] valid) {
        if (startIndex == s.length()) {
            res.add(new ArrayList<>(tmp));
            return;
        }
        for (int i = startIndex; i < s.length(); ++i) {
            if (valid[startIndex][i] == false) {
                continue;
            }
            tmp.add(s.substring(startIndex, i + 1));
            dfs(s, i + 1, tmp, res, valid);
            tmp.remove(tmp.size() - 1);
        }
    }
}