java算法(1)

原题:

// Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results.// Note: The input string may contain letters other than the parentheses ( and ).// Examples:// "()())()" -> ["()()()", "(())()"]// "(a)())()" -> ["(a)()()", "(a())()"]// ")(" -> [""]

答案:

public class Solution {    public List<String> removeInvalidParentheses(String s) {        List<String> result = new ArrayList<>();        remove(s, result, 0, 0, new char[]{'(', ')'});        return result;    }    public void remove(String s, List<String> result, int last_i, int last_j,  char[] par) {        for (int stack = 0, i = last_i; i < s.length(); i++) {            if (s.charAt(i) == par[0]) stack++;            if (s.charAt(i) == par[1]) stack--;            if (stack >= 0) continue;            for (int j = last_j; j <= i; j++)                if (s.charAt(j) == par[1] && (j == last_j || s.charAt(j - 1) != par[1]))                    remove(s.substring(0, j) + s.substring(j + 1, s.length()), result, i, j, par);            return;        }        String reversed = new StringBuilder(s).reverse().toString();        if (par[0] == '(') // finished left to right            remove(reversed, result, 0, 0, new char[]{')', '('});        else // finished right to left            result.add(reversed);    }}