Insert Interval & *Regular Expression Matching & Binary Tree Maximum Path Sum

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(1) Insert Interval

利用merge intervals的成果：

bool comp(Interval a,Interval b) {        return a.start < b.start;    } class Solution {private:    vector<Interval> merge(vector<Interval> &intervals) {                sort(intervals.begin(), intervals.end(), comp);                if(intervals.size()<=1)            return intervals;                vector<Interval>::iterator t1=intervals.begin(),t2=t1+1;                while(t1!=intervals.end() && t2!=intervals.end())        {            if(t1->end >= t2->start)            {                t1->end= max(t1->end,t2->end);                t2++;                }            else            {                t1=intervals.erase(t1+1,t2);                t2=t1+1;            }        }                if(t1!=intervals.end())            intervals.erase(t1+1,t2);                return intervals;    }public:    vector<Interval> insert(vector<Interval> &intervals, Interval newInterval) {        intervals.push_back(newInterval);                return merge(intervals);    }};

(2) Regular Expression Matching

对于S[i]和P[j]：
如果P[j+1]!='*'，S[i] == P[j]=>匹配下一位(i+1, j+1)，S[i]!=P[j]=>匹配失败；
如果P[j+1]=='*'，S[i]==P[j]=>匹配下一位(i+1, j+2)或者(i, j+2)，S[i]!=P[j]=>匹配下一位(i,j+2)。
匹配成功的条件为S[i]=='\0' && P[j]=='\0'。[1]

class Solution {public:    bool isMatch(const char *s, const char *p) {        if(*p=='\0')            return *s=='\0';                if(*(p+1)=='*')        {            while(*s!='\0' && (*s==*p || *p=='.'))            {                if(isMatch(s,p+2))                    return true;                s++;            }            return isMatch(s,p+2);        }        else        {            if(*s!='\0' && (*s==*p || *p=='.'))                return isMatch(s+1,p+1);        }        return false;    }};

(3) Binary Tree Maximum Path Sum

递归计算每个节点的Maximum Path Sum：[2]

class Solution {private:    int recursive(TreeNode *root, int &Max) {        if(root==NULL)            return 0;                int leftMax=recursive(root->left,Max);        int rightMax=recursive(root->right,Max);        int rootMax=leftMax+root->val+rightMax;        int RootToParentMax=max(root->val,max(leftMax,rightMax)+root->val);        Max=max(Max,max(rootMax,RootToParentMax));        return RootToParentMax;    }public:    int maxPathSum(TreeNode *root) {        int Max=-32767;        recursive(root,Max);        return Max;    }};

参考：

[1] http://blog.csdn.net/pickless/article/details/9043389

[2] http://blog.csdn.net/fightforyourdream/article/details/16894069

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