JAVA - 根据用户自增ID生成邀请码的工具类

约定不等于承诺〃 2022-12-22 09:18 161阅读 0赞

/**
     * 根据用户ID生成邀请码的工具类
     */
    public class GetCodeUtil {
    
        public static void main(String[] args) {
            String code = encode(132456);
            int nid = decode(code);
            System.out.println(  132456 + " -> " + code + " -> " + nid);
        }
    
        //验证码长度
        private static final int LEN = 6;
        //验证码字符列表
        private static final char STUFFS[] = {
                'A','B','C','D','E','F','G','H',
                'I','J','K','L','M','N','P','Q',
                'R','S','T','U','V','W','X','Y',
                '1','2','3','4','5','6','7','8'};
    
        private static final int PERMUTATION;
        private static final int MAX_COMBINATION;
    
        static {
            PERMUTATION = permutation(LEN);
            MAX_COMBINATION = combination(STUFFS.length,LEN);
        }
    
        private static int combination(int n,int m) {
            int com = 1;
            for(int i = n - m + 1; i <= n ; ++i) {
                com *= i;
            }
            for(int i = 2; i <= m ; ++i ) {
                com /= i;
            }
            return com;
        }
    
        private static int permutation(int n) {
            int per = 1;
            for(int i = 2; i <= n ; ++i) {
                per *= i;
            }
            return per;
        }
    
        public static int decode(String code) {
            if(code.length() != LEN) {
                throw new RuntimeException("invalid code");
            }
            char[] chars = new char[LEN];
            for(int i = 0; i < LEN;++i) {
                chars[i] = code.charAt(i);
            }
            int com = combination(chars);
            int per = permutation(chars);
            return com * PERMUTATION + per;
        }
    
        public static String encode(int val) {
            int com = val / PERMUTATION;
            if(com >= MAX_COMBINATION) {
                throw new RuntimeException("id can't be greater than 652458239");
            }
            int per = val % PERMUTATION;
            char[] chars = combination(com);
            chars = permutation(chars,per);
            return new String(chars);
        }
    
        private static char[] combination(int com){
            char[] chars = new char[LEN];
            int start = 0;
            int index = 0;
            while (index < LEN) {
                for(int s = start; s < STUFFS.length; ++s ) {
                    int c = combination(STUFFS.length - s - 1, LEN - index - 1);
                    if(com >= c) {
                        com -= c;
                        continue;
                    }
                    chars[index++] = STUFFS[s];
                    start = s + 1;
                    break;
                }
            }
            return chars;
        }
    
        private static char[] sort(char[] src) {
            char[] sort = new char[src.length];
            int index = 0;
            for(int i = 0; i < STUFFS.length;++i) {
                if(find(src, STUFFS[i]) != -1) {
                    sort[index++] = STUFFS[i];
                }
            }
            return sort;
        }
    
        private static int combination(char[] chars) {
            int[] offset = new int[LEN];
            char[] sort = sort(chars);
            for(int i = 0; i < sort.length;++i) {
                offset[i] = find(STUFFS, sort[i]);
                if(offset[i] == -1) {
                    throw new RuntimeException("invalid code");
                }
            }
            int com = 0;
            for(int i = 0;i < offset.length;++i) {
                if(i == 0) {
                    if(offset[0] == 0) {
                        continue;
                    }
                    for(int n = 0; n < offset[0];++n) {
                        com += combination(STUFFS.length -  n - 1, LEN - 1);
                    }
                    continue;
                }
    
                if(offset[i] - offset[i - 1] <= 1) {
                    continue;
                }
    
                for(int n = offset[i-1] + 1; n < offset[i];++n) {
                    com += combination(STUFFS.length -  n - 1, LEN - i - 1);
                }
            }
    
            return com;
        }
    
        private static char[] permutation(char[] chars,int per){
            char[] tmpchars = new char[chars.length];
            System.arraycopy(chars, 0, tmpchars, 0, chars.length);
            int[] offset = new int[chars.length];
            int step = chars.length;
            for(int i = chars.length -1;i >= 0;--i) {
                offset[i] = per % step;
                per /= step;
                step --;
            }
    
            for(int i = 0; i < chars.length;++i) {
                if(offset[i] == 0)
                    continue;
                char tmp = tmpchars[i];
                tmpchars[i] = tmpchars[i - offset[i]];
                tmpchars[i - offset[i]] = tmp;
            }
    
            return tmpchars;
        }
    
        private static int find(char[] chars,char ch) {
            for(int i = 0;i < chars.length;++i) {
                if(chars[i] == ch) {
                    return i;
                }
            }
            return -1;
        }
    
        private static int permutation(char[] chars){
            char[] sort = sort(chars);
            int[] offset = new int[chars.length];
            for(int i =chars.length -1;i >=0;--i ) {
                int f = find(chars, sort[i]);
                offset[i] = i - f;
                char tmp = chars[i];
                chars[i] = chars[i - offset[i]];
                chars[i - offset[i]] = tmp;
            }
            int per = 0;
            int step = 1;
            for(int i = 0; i < offset.length;++i ) {
                per = per * step + offset[i];
                step++;
            }
            return per;
        }
    
    
    }