leetcode：Restore IP Addresses

最新推荐文章于 2022-08-09 17:22:07 发布

SCAU啊源

最新推荐文章于 2022-08-09 17:22:07 发布

阅读量445

点赞数

CC 4.0 BY-SA版权

分类专栏： leetcode

本文链接：https://blog.youkuaiyun.com/chanrenyuan/article/details/30990839

leetcode 专栏收录该内容

168 篇文章

订阅专栏

本文深入探讨了如何使用深度优先搜索（DFS）解决IP地址组合问题，通过示例展示算法实现，包括边界条件判断和递归过程，最终返回所有有效的IP地址组合。

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

For example:
Given "25525511135",

return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)

直接DFS了

public class Solution {
    
        static char[] str;
        static ArrayList<String> ans = new ArrayList<String>();

        public ArrayList<String> restoreIpAddresses(String s) {
            ArrayList<Integer> stack = new ArrayList<Integer>();
            ans.clear();
            str = s.toCharArray();
            dfs(stack, 0, 0);
            return ans;
        }

        static void dfs(ArrayList<Integer> stack, int dept, int pos) {
            if (dept == 4 && pos == str.length) {
                ans.add(getIP(stack));
            } else if (dept < 4 && pos < str.length) {
                
                for (int i = pos; i < str.length; ++i) {
                    if(str[pos] == '0' && pos != i)
                        return;
                    int temp = getNum(pos, i + 1);
                    if (temp <= 255) {
                        stack.add(temp);
                        dfs(stack, dept + 1, i + 1);
                        stack.remove(dept);
                    } else {
                        break;
                    }
                }
            }
        }

        static int getNum(int start, int end) {
            int num = 0;
            for (int i = start; i < end; ++i) {
                num *= 10;
                num += str[i] - '0';
            }
            return num;
        }

        static String getIP(ArrayList<Integer> stk) {
            String s = "";
            s += stk.get(0);
            for (int i = 1; i < stk.size(); ++i) {
                s += ".";
                s += stk.get(i);
            }
            return s;
        }
}