A typical example using STL

Isenbaev/Source.cpp

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+//
+//  main.cpp
+//  Isenbaev
+//
+//  Created by Nicholas.L.Y on 2016/5/9.
+//  Copyright © 2016 廖颖泓. All rights reserved.
+//
+#include <iostream>
+#include <map>
+#include <string>
+#include <vector>
+#include <set>
+#include <queue>
+#include <vld.h>
+using namespace std;
+const string god = "Isenbaev";
+int main() {
+    int n;
+    cin >> n;
+    map<string, set<string> > teammate;
+    for (int i = 0; i < n; i++) {
+        string s[3];
+        for (int j = 0; j < 3; j++) cin >> s[j];
+        for (int j = 0; j < 3; j++) {
+            for (int k = 0; j < 3; j++) {
+                if (j == k) continue;
+                teammate[s[j]].insert(s[k]);
+            }
+        }
+    }
+    map<string, set<string> >::iterator iter;
+    set<string>::iterator its;
+    map<string, int> dis;
+    for (iter = teammate.begin(); iter != teammate.end(); iter++) {
+        dis[iter->first] = -1;
+    }
+    queue<string> q;
+    set<string> all;
+    if (teammate.find(god) != teammate.end()) {
+        dis[god] = 0;
+        q.push(god);
+        all.insert(god);
+    }
+    while (!q.empty()) {
+        string temp = q.front();
+        q.pop();
+        int temp_dis = dis[temp];
+        for (its = teammate[temp].begin(); its != teammate[temp].end(); its++) {
+            if (all.find(*its) != all.end()) continue;
+            all.insert(*its);
+            dis[*its] = temp_dis + 1;
+            q.push(*its);
+        }
+    }
+    map<string, int>::iterator it;
+    for (it = dis.begin(); it != dis.end(); it++) {
+        cout << it->first << ' ';
+        if (it->second == -1) cout << "undefined" << endl;
+        else cout << it->second << endl;
+    }
+    return 0;
+}