正则表达式匹配

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public class Solution {
    public boolean match (String str, String pattern) {
        int m = str.length(), n = pattern.length();
        boolean[][] dp = new boolean[m + 1][n + 1];
        dp[0][0] = true;
        for(int i = 0; i <= m; i++){
            for(int j = 1; j <= n; j++){
                if(pattern.charAt(j - 1) != '*'){
                    if(i > 0 && (str.charAt(i - 1) == pattern.charAt(j - 1) || pattern.charAt(j - 1) == '.')){
                        dp[i][j] = dp[i - 1][j - 1];
                    }
                }else{
                    boolean dp1 = false;
                    boolean dp2 = false;
                    if(j >= 2){
                        dp1 = dp[i][j - 2];
                    }
                    if(i > 0 && j >= 2 && (str.charAt(i - 1) == pattern.charAt(j - 2) || pattern.charAt(j - 2) == '.')){
                        dp2 = dp[i - 1][j];
                    }    
                    dp[i][j] = dp1 || dp2;
                }
            }
        }
        return dp[m][n];
    }
}

反转链表(递归)

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public class Solution {
    public ListNode ReverseList(ListNode head) {
        return reverse(head, null);
    }
    
    private ListNode reverse(ListNode cur, ListNode pre){
        if(cur == null){
            return pre;
        }
        // cur.next为下一次递归的cur, 而这次的cur随着下一次的递归变成了下一次的pre
        ListNode res = reverse(cur.next, cur);
        cur.next = pre;
        return res;
    }
}