程序员面试金典 - 面试题 17.17. 多次搜索（Trie树）

示例：
输入：
big = "mississippi"
smalls = ["is","ppi","hi","sis","i","ssippi"]
输出： [[1,4],[8],[],[3],[1,4,7,10],[5]]

提示：
0 <= len(big) <= 1000
0 <= len(smalls[i]) <= 1000
smalls的总字符数不会超过 100000。
你可以认为smalls中没有重复字符串。
所有出现的字符均为英文小写字母。

class Solution {
public:
    vector<vector<int>> multiSearch(string big, vector<string>& smalls) {
    	unordered_map<char,vector<int>> m;
    	int i, j, n = smalls.size();
    	bool found;
    	vector<vector<int>> ans(n);
    	for(i = 0; i < big.size(); ++i)
    		m[big[i]].push_back(i);//每个字符开始的位置
    	for(i = 0; i < n; ++i)
    	{
    		if(smalls[i].empty())
    			continue;
    		for(auto idx : m[smalls[i][0]])//每个small单词开始的字符在big里的位置
    		{
    			found = true;
    			if(big.size()-idx < smalls[i].size())
    				break;
    			for(j = 0; j < smalls[i].size(); ++j)
    			{	//对big中每个开始的位置开始向后查找small
    				if(big[idx+j] != smalls[i][j])
    				{
    					found = false;
    					break;
    				}
    			}
    			if(found)
    				ans[i].push_back(idx);
    		}
    	}
    	return ans;
    }
};

class trie
{
public:
	bool isEnd = false;
	trie* next[26] = {NULL};
	void insert(string& s)
	{
		trie *cur = this;
		for(int i = 0; i < s.size(); ++i)
		{
			if(!cur->next[s[i]-'a'])
				cur->next[s[i]-'a'] = new trie();
			cur = cur->next[s[i]-'a'];
		}
		cur->isEnd = true;
	}
};
class Solution {
public:
    vector<vector<int>> multiSearch(string big, vector<string>& smalls) {
    	trie* t = new trie();
    	unordered_map<string,int> m;
    	int i, j, n = smalls.size();
    	bool found;
    	vector<vector<int>> ans(n);
    	for(i = 0; i < n; ++i)
    		m[smalls[i]] = i;
    	for(i = 0; i < n; ++i)
    		t->insert(smalls[i]);
    	string s;
    	trie* cur;
    	for(i = 0; i < big.size(); ++i)
    	{
    		s = "";
    		cur = t;
    		for(j = i; j < big.size(); ++j)
    		{
    			if(!cur->next[big[j]-'a'])
    				break;
    			s += big[j];
    			cur = cur->next[big[j]-'a'];
    			if(cur->isEnd)
    				ans[m[s]].push_back(i);
    		}
    	}
    	return ans;
    }
};