还原IP地址.java

package com.raylew.algorithm.book1;

/*
 将一个字符串还原成ip地址
 */
public class 还原IP地址 {
    //可还原的ip地址个数
    public static int total = 0;
    //测试数据：指定字符串
    public static String ip = "25525511135";
    //存放可能的ip地址
    public static String[] temp = new String[4];

    public static void main(String[] args) {
        dfs(0);
        System.out.println(total);
    }

    /**
     * dfs算法
     *
     * @param cur ip地址中的第cur节
     */
    public static void dfs(int cur) {
        if (cur == 4) {
            int len = 0;
            for (int i = 0; i < 4; i++) {
                len += temp[i].length();
            }
            if (len != ip.length()) {
                return;
            }
            int i;
            for (i = 0; i < 4; i++) {
                if (Integer.parseInt(temp[i]) > 255) {
                    break;
                }
            }
            if (i == 4) {
                total++;
                for (int j = 0; j < 4; j++) {
                    System.out.print(temp[j] + ".");
                }
                System.out.println();
            }
            return;
        }
        String backup = ip;
        for (int i = 1; i <= 3; i++) {
            int len = 0;
            for (int j = 0; j < cur; j++) {
                len += temp[j].length();
            }
            if ((len + i) <= ip.length()) {
                temp[cur] = backup.substring(len, (len + i));
                dfs(cur + 1);
            }
        }
    }
}