题解 | #验证IP地址# 注意16进制与split的用法

import java.util.*;


public class Solution {
    /**
     * 验证IP地址
     * @param IP string字符串 一个IP地址字符串
     * @return string字符串
     */
    public String solve (String IP) {
	  	//最后一位是 . split会忽略
        if (IP.contains(".") && IP.lastIndexOf(".") != IP.length() - 1) {
            //是IPv4 或者 Neither
            boolean isOK = true;
            String[] ips = IP.split("\\.");
            if (ips.length == 4) {
                for (int i = 0; i < ips.length; i++) {
                    String cur = ips[i];
                    if ("".equals(cur)) {
                        isOK = false;
                        break;
                    } else if (cur.startsWith("0") && cur.length() > 1) {
                        isOK = false;
                        break;
                    } else {
                        if (!isInteger(cur)) {
                            isOK = false;
                            break;
                        }
                        int value = Integer.valueOf(cur);
                        if (value < 0 || value > 255) {
                            isOK = false;
                            break;
                        }
                    }
                }
            } else {
                isOK = false;
            }
            if (isOK) {
                return "IPv4";
            } else {
                return "Neither";
            }
        } else if (IP.contains(":") && IP.lastIndexOf(":") != IP.length() - 1) {
            //是IPv6 或者 Neither
            boolean isOK = true;
            String[] ips = IP.split(":");
            if (ips.length == 8) {
                for (int i = 0; i < ips.length; i++) {
                    String cur = ips[i];
                    if ("".equals(cur)) {
                        isOK = false;
                        break;
                    } else if (cur.length() > 4 || !isLegal(cur)) {
                        isOK = false;
                        break;
                    }
                }
            } else {
                isOK = false;
            }
            if (isOK) {
                return "IPv6";
            } else {
                return "Neither";
            }

        } else {
            return "Neither";
        }
    }

    private boolean isInteger(String s) {
        char[] chars = s.toCharArray();
        for (int i = 0; i < chars.length ; i++) {
            char cur = chars[i];
            if (cur > '9' || cur < '0') {
                return false;
            }
        }
        return true;
    }

    private boolean isLegal(String s) {
        char[] chars = s.toCharArray();
        for (int i = 0; i < chars.length ; i++) {
            char cur = chars[i];
            boolean isOk = false;
            if ((cur >=0 && cur <= '9') || (cur >= 'a' && cur <= 'f') || (cur >= 'A' && cur <= 'F')) {
                isOk = true;
            }
            if(!isOk){
                return false;
            }
        }
        return true;
    }
}