给定无序数组，求最大的连续的数的长度

class Solution {
public:
    int longestConsecutive(vector<int> &num) {
        map<int, bool> flagMap;
        int nMaxLen = 1;
        
        for (vector<int>::iterator itr=num.begin(); itr!=num.end();++itr)
            flagMap[*itr] = true;
            
        for (vector<int>::iterator itr=num.begin(); itr!=num.end();++itr)
        {
            int nCount = 1;
            if (flagMap[*itr])
            {
                flagMap[*itr] = false;      // mark false
                
                int nLeft = *itr-1;
                while (flagMap.find(nLeft)!=flagMap.end() && flagMap[nLeft]){
                    flagMap[nLeft] = false;
                    ++nCount;
                    nLeft -= 1;
                }
                
                int nRight = *itr + 1;
                while (flagMap.find(nRight)!=flagMap.end() && flagMap[nRight]){
                    flagMap[nRight] = false;
                    ++nCount;
                    nRight += 1;
                }
            }
            
            if (nCount > nMaxLen)
            nMaxLen = nCount;
        }
        
        return nMaxLen;
    }
    
};