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

(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