Hackerrank (1): CodeStorm 2015 > Little Alexey's Tree

题目：

Problem Statement

Little Alexey was playing with trees while studying powerful tree algorithms.

Recently, he discovered a tree with n vertices. On each edge, there's a lowercase English letter written on it.

If we concatenate all the letters on the path from vertex u to vertex v, we can write some word. Little Alexey is interested in the largest lexicographical words.

For every vertex u, find a vertex v to create a string that is lexicographically largest by concatenating all the letters on the path fromu to v. If the vertices are lexicographically the same size, find the one with the largest number.

Input Format

On the first line, you are given a single positive integer n: the number of vertices in the tree.Each of the next n−1 lines contains space-separated positive integers ai,bi and a character ci, that describes an edge between ai and bi with ci written on the edge.

Constraints

1≤n≤2⋅104
1≤ai,bi≤n
ci is a lowercase English letter

Output Format

Print n space-separated positive integers: the answer for the task.

Sample Input 1

41 2 a2 3 a3 4 b

Sample Output 1

4 4 4 1

Sample Input 2

91 2 b2 3 a2 4 c1 6 c6 5 d6 7 c1 9 d9 8 e

Sample Output 2

8 4 4 8 8 5 5 5 8

Explanation

Let's look at the first sample. A way between 1 and 4 corresponds to string ′aab′. A way between 2 and 4 corresponds to ′ab′. A way between 3 and 4 corresponds to ′b′. A way between 4 and 1 corresponds to ′baa′. It's easy to see that these paths are the lexicographically largest.

题解：

通过了22个Case，还有36个Case超时，算法应该是对的。

C++版：

#include <cmath>#include <cstdio>#include <vector>#include <iostream>#include <algorithm>#include <unordered_map>#include <set>#include <stack>using namespace std;struct comparator {    bool operator() (const pair<int, char>& a, const pair<int, char>& b) {        return a.second >= b.second;    }};int main() {    /* Enter your code here. Read input from STDIN. Print output to STDOUT */    int numberOfLines;    cin >> numberOfLines;    if(numberOfLines == 1) {        cout << 1 << endl;        return 0;    }    unordered_map<int, set<pair<int, char>, comparator>> tree;    for(int i = 0; i < numberOfLines - 1; i++) {        int start, end;        char c;        cin >> start >> end >> c;        if(tree.find(start) == tree.end()) {            set<pair<int, char>, comparator> edges;            edges.insert(pair<int, char>(end, c));            tree.insert(pair<int, set<pair<int, char>, comparator>>(start, edges));        } else {            set<pair<int, char>, comparator> s = tree[start];            s.insert(pair<int, char>(end, c));            tree[start].insert(pair<int, char>(end, c));        }        if(tree.find(end) == tree.end()) {            set<pair<int, char>, comparator> edges;            edges.insert(pair<int, char>(start, c));            tree.insert(pair<int, set<pair<int, char>, comparator>>(end, edges));        } else {            tree[end].insert(pair<int, char>(start, c));        }    }        for(int i = 1; i <= numberOfLines; i++) {        vector<pair<string, int>> results;        stack<pair<pair<int, int>, string>> path;        auto iter = tree[i].begin();        string s = "";        char c = iter->second;        s += c;        do {            pair<int, int> p(iter->first, i);            path.push(pair<pair<int, int>, string>(p, s));            iter++;        } while (iter != tree[i].end() && iter->second == c);        while(!path.empty()) {            int cur = path.top().first.first;            int last = path.top().first.second;            string curS = path.top().second;                        path.pop();                        auto iter2 = tree[cur].begin();            if(iter2->first == last)                iter2++;            if(iter2 == tree[cur].end()) {                results.push_back(pair<string, int>(curS, cur));                continue;            }            char c1 = iter2->second;            curS += c1;            for(iter2; iter2 != tree[cur].end() && iter2->second == c1; iter2++) {                if(iter2->first == last)                    continue;                pair<int, int> p(iter2->first, cur);                path.push(pair<pair<int, int>, string>(p, curS));            }        }        string largestS = "";        int largestI = 0;        for(int j = 0; j < results.size(); j++) {            if(results[j].first == largestS) {                largestI = max(largestI, results[j].second);            } else if(results[j].first > largestS) {                largestS = results[j].first;                largestI = results[j].second;            }        }        cout << largestI << " ";    }        return 0;}