LeetCodev379. Design Phone Directory

Design a Phone Directory which supports the following operations:

get: Provide a number which is not assigned to anyone.
check: Check if a number is available or not.
release: Recycle or release a number.
Example:

// Init a phone directory containing a total of 3 numbers: 0, 1, and
2. PhoneDirectory directory = new PhoneDirectory(3);

// It can return any available phone number. Here we assume it returns
0. directory.get();

// Assume it returns 1. directory.get();

// The number 2 is available, so return true. directory.check(2);

// It returns 2, the only number that is left. directory.get();

// The number 2 is no longer available, so return false.
directory.check(2);

// Release number 2 back to the pool. directory.release(2);

// Number 2 is available again, return true. directory.check(2);

s思路：
1. 设计题，最开始想到可以用unordered_set
2. 参考http://www.cnblogs.com/grandyang/p/5735205.html 不用set或queue或stack,都会TLE。这种情况下，说明可以直接用vector来模拟这些复杂的数据结构，两个vector,一个放回收的数据，方便o(1)取数据；一个放数据是否存在pool的flag，方便o(1)查询是否存在！！！不得不说很高级很简洁啊！

//方法1：用unordered_set来做，所有操作o(1)。最大的问题是constructor需要o(n)的时间，但是每次get的时候，又是依次输出，所以完全可以用一个递增的变量代替目前get那个位置了，而不用傻头傻脑的把如此规则的数先存起来再取，时间太慢！！！class PhoneDirectory {public:    /** Initialize your data structure here        @param maxNumbers - The maximum numbers that can be stored in the phone directory. */    PhoneDirectory(int maxNumbers) {        maxNum=maxNumbers;        for(int i=0;i<maxNum;i++)            ss.insert(i);    }    /** Provide a number which is not assigned to anyone.        @return - Return an available number. Return -1 if none is available. */    int get() {        if(ss.size()>0){            int cur=*ss.begin();            ss.erase(cur);            return cur;        }        return -1;    }    /** Check if a number is available or not. */    bool check(int number) {        if(number>=0&&number<maxNum&&ss.count(number))            return true;        return false;    }    /** Recycle or release a number. */    void release(int number) {        if(number>=0&&number<maxNum)            ss.insert(number);    }private:    unordered_set<int> ss;    int maxNum;};//方法2：用一个变量next来保存取的数据，把release的数据放在一个新的vector或queue内，然后用一个vector<bool>做标记，表名某一个值在pool内。class PhoneDirectory {public:    /** Initialize your data structure here        @param maxNumbers - The maximum numbers that can be stored in the phone directory. */    PhoneDirectory(int maxNumbers) {        maxNum=maxNumbers;        next=0;        index=0;        pool.resize(maxNum);        flag.resize(maxNum,1);//初始化表明所有数都有！    }    /** Provide a number which is not assigned to anyone.        @return - Return an available number. Return -1 if none is available. */    int get() {        if(next==maxNum&&index<=0) return -1;        if(index>0){            int cur=pool[--index];            flag[cur]=0;            return cur;         }        if(next<maxNum){            flag[next]=0;            return next++;          }    }    /** Check if a number is available or not. */    bool check(int number) {        if(number>=0&&number<maxNum&&flag[number])            return true;        return false;        //以上三句可以浓缩成一句：        return (number>=0&&number<maxNum&&flag[number]);    }    /** Recycle or release a number. */    void release(int number) {        if(number>=0&&number<maxNum&&flag[number]==0){            pool[index++]=number;            flag[number]=1;        }    }private:    vector<int> pool;    vector<bool> flag;    int maxNum;    int next,index;};