Longest Common Prefix

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-----QUESTION-----

Write a function to find the longest common prefix string amongst an array of strings.

-----SOLUTION-----

class Solution {public:    string longestCommonPrefix(vector&strs) {        if(strs.empty()) return "";        if(strs.size() == 1) return strs[0];        int maxPrefix = strs[0].length();        for(int i=1; i            maxPrefix = min(maxPrefix, (int)strs[i].length());            for(int j =0; j < maxPrefix; j++){ //traverse the character in the string                if(strs[i][j]!=strs[0][j]) maxPrefix = min(maxPrefix, j);            }        }        if(maxPrefix == 0 ) return "";        return strs[0].substr(0,maxPrefix);    }};

解法II：使用字典树

class Solution {public:    // definition of TreeNode    struct TreeNode{        char ch;            // character of the node        int count;            // number of strings        vector children;    // children of this node        TreeNode() : ch ('$'), count(1){}        TreeNode(char c) : ch(c){count = 1;}    };       // definition of Trie    struct Trie{        TreeNode* root;                // root node of the Trie           // default constructor        Trie(){            root = new TreeNode('$');        }           // destructor        ~Trie(){            destroy(root);        }           // destroy the Trie        void destroy(TreeNode* &node){            if(node != NULL){                for(int i = 0; i < node->children.size(); ++i){                    destroy(node->children[i]);                }                delete node;            }        }           // insert a string into the Trie        void insert(TreeNode* &node, string str){            // null node or empty string            if(node == NULL || str == ""){                return;            }               // search the node            for(int i = 0; i < node->children.size(); ++i){                // found it                if(node->children[i]->ch == str[0]){                    (node->children[i]->count)++;                    insert(node->children[i], str.substr(1, str.length()-1));                    return;                }            }               // a new node of the node            TreeNode* child = new TreeNode(str[0]);            node->children.push_back(child);            insert(child, str.substr(1, str.length()-1));        }           // get longest common prefix        vector getLongest(TreeNode* &node, int count){            vector res;               // null node            if(node == NULL || count <= 0){                return res;            }            if(node != root && node->count < count){                return res;            }               // search in its children            if(node->children.size() > 0){                // generate head                char tmp[2];                tmp[0] = node->ch;                tmp[1] = '\0';                string head(tmp);                   for(int i = 0; i < node->children.size(); ++i){                    vector r = getLongest(node->children[i], count);                    for(int j = 0; j < r.size(); ++j){                        res.push_back(head + r[j]);                    }                }                   // there is no common prefix in it children, add itself                if(res.size() <= 0){                    res.push_back(head);                }            }            else{                char tmp[2];                tmp[0] = node->ch;                tmp[1] = '\0';                res.push_back(tmp);            }               return res;        }           // print Trie        void print(TreeNode* &node){            // null node            if(node == NULL){                return;            }               // print itself            cout << "[" << node->ch << "," << node->count << "] ";               // print its children            for(int i = 0; i < node->children.size(); ++i){                print(node->children[i]);            }               // print a endl            if(node == root){                cout << endl;            }        }    };       // longest common prefix    string longestCommonPrefix(vector &strs) {        // Start typing your C/C++ solution below        // DO NOT write int main() function               // empty input        if(strs.size() <= 0){            return "";        }           // create Trie            Trie* trie = new Trie();        for(int i = 0; i < strs.size(); ++i){            trie->insert(trie->root, strs[i]);        }           // print Trie        // trie->print(trie->root);           // get longest common prefix        string longest = "";        vector res = trie->getLongest(trie->root, strs.size());        for(int i = 0; i < res.size(); ++i){            // NOTE: remove the root node '$'            if(res[i].length() - 1 > longest.length()){                longest = res[i].substr(1, res[i].length()-1);            }        }           // delete Trie        delete trie;           return longest;    }};

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