diff --git a/.gitignore b/.gitignore
index 259148fa18f9fb7ef58563f4ff15fc7b172339fb..d333e34ee0e5217d1e51f54114ccb7da48f4565a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -30,3 +30,8 @@
 *.exe
 *.out
 *.app
+info.plist
+
+#patch
+*.patch
+*.dff
\ No newline at end of file
diff --git a/README.md b/README.md
index 46e56744aadc284d9f12caca11c085ab64391ad9..8402c5fdbd8a3573f61d4e858a5b201c0fb74610 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,4 @@
 # leetcode
 
-## 题目
+## BFS
+[815. 公交路线](https://leetcode-cn.com/problems/bus-routes/)
\ No newline at end of file
diff --git a/include/stl.h b/include/stl.h
new file mode 100644
index 0000000000000000000000000000000000000000..0d21a8ef98c1782ff1fd607613afb7e568d659b1
--- /dev/null
+++ b/include/stl.h
@@ -0,0 +1,3 @@
+#pragma once
+#include "virtualio.h"
+using namespace std;
diff --git a/include/virtualio.h b/include/virtualio.h
new file mode 100644
index 0000000000000000000000000000000000000000..ad61c12494401cfc4011884c09600f6eb62eae2a
--- /dev/null
+++ b/include/virtualio.h
@@ -0,0 +1,75 @@
+#pragma once
+#include <cstdio>
+#include <iostream>
+#include <sstream>
+#include <string>
+#include <vector>
+#include <list>
+#include <set>
+#include <map>
+#include <unordered_map>
+
+#define print(...) print_any(__VA_ARGS__);
+
+class VOut{
+public:
+    virtual std::string str() {return "";}
+};
+
+template<class ostream_t>
+class OStream : public VOut {
+public:
+    ostream_t out;
+    ostream_t *po;
+    OStream() { po = &out; }
+    OStream(ostream_t o) : out(o){ po = &out; }
+    OStream(ostream_t * o) : po(o){}
+    OStream& operator<<(const char*t){(*po)<<t; return *this;}
+    template<class T> OStream& operator<<(const T&t){(*po)<< t; return *this;}
+    template<class T> OStream& operator<<(const T*t){(*po)<<*t; return *this;}
+    template<class T> OStream& operator<<(const std::vector<T> &v){
+        return Out(v.begin(), v.end());
+    }
+    template<class T> OStream&operator<<(const std::list<T> &v){
+        return Out(v.begin(), v.end());
+    }
+    template<class T> OStream& operator<<(const std::set<T> &v){
+        return Out(v.begin(), v.end());
+    }
+    template<class K, class V> OStream& operator<<(const std::pair<K,V> & pair){
+        (*this) << pair.first;
+        (*po) << '=';
+        (*this) << pair.second;
+        return *this;
+    }
+    template<class K, class V> OStream&operator<<(const std::unordered_map<K,V> &m){
+        return Out(m.begin(), m.end());
+    }
+    template<class K, class V> OStream&operator<<(const std::map<K,V> &m){
+        return Out(m.begin(), m.end());
+    }
+protected:
+    template<class iterator>
+    OStream& Out(iterator src, iterator dst){
+        auto p = src;
+        if(p != dst)   {(*po)<< '['; (*this)<<*p;}
+        while(++p!=dst){(*po)<<", "; (*this)<<*p;}
+        if(p != src)   (*po)<< ']';
+        return *this;
+    }
+};
+
+class StrStream : public OStream<std::stringstream>
+{
+public:
+    virtual std::string str() override{
+        return out.str();
+    }
+};
+
+template<class ...Any>
+inline void print_any(const Any ...any){
+    StrStream ss;
+    std::initializer_list<bool>{(ss << any, true)...}.size();
+    std::cout << ss.str();
+}
\ No newline at end of file
diff --git "a/questions/815. \345\205\254\344\272\244\350\267\257\347\272\277/main.cpp" "b/questions/815. \345\205\254\344\272\244\350\267\257\347\272\277/main.cpp"
new file mode 100644
index 0000000000000000000000000000000000000000..675fbdd5f9d96fe827ec798629dad8e283a94648
--- /dev/null
+++ "b/questions/815. \345\205\254\344\272\244\350\267\257\347\272\277/main.cpp"	
@@ -0,0 +1,13 @@
+#include "stl.h"
+#include "solution.h"
+
+int main(int argc, char *argv[]){
+    vector<vector<int>> routes = {
+        {1,2,7},
+        {3,6,7},
+    };
+    int source = 1, target = 6;
+    int result = Solution().numBusesToDestination(routes, source, target);
+    print("result=", result);
+    return 0;
+}
\ No newline at end of file
diff --git "a/questions/815. \345\205\254\344\272\244\350\267\257\347\272\277/solution.h" "b/questions/815. \345\205\254\344\272\244\350\267\257\347\272\277/solution.h"
new file mode 100644
index 0000000000000000000000000000000000000000..c9353a7d25854e4f1a760b95cb6e033bda216c55
--- /dev/null
+++ "b/questions/815. \345\205\254\344\272\244\350\267\257\347\272\277/solution.h"	
@@ -0,0 +1,67 @@
+// #define print(...)
+#define map_t unordered_map
+struct SearchInfo{
+    // 搜索过的线路
+    list<int> ln;
+    // <line, transfer_times> 到达每条线所需换乘次数
+    map_t<int, int> jmp;
+};
+class Solution {
+    SearchInfo infos[2];
+    // <line, points> 各条线上的站点
+    std::vector<std::set<int>> l2p;
+    // <point, lines> 各个站点可换乘的线路
+    map_t<int, std::set<int>> p2l;
+public:
+    int numBusesToDestination(vector<vector<int>>& routes, int source, int target) {
+        print(routes, "\n")
+        if(source == target) return 0;
+        // init map 
+        l2p.reserve(routes.size());
+        l2p.resize(routes.size());
+        for(int l=0; l<routes.size(); l++){
+            auto &pts = routes[l];
+            for(auto &p : pts)
+                p2l[p].insert(l);
+            l2p[l].insert(pts.begin(), pts.end());
+        }
+        auto & sl = p2l[source];
+        for(auto &l : p2l[target]){
+            if(sl.count(l)) return 1;
+        }
+        // terminal lines
+        int peers[] = {source, target};
+        for(int i=0; i<2; i++){ // src, dst
+            auto &lns = p2l[peers[i]];
+            infos[i].ln.insert(infos[i].ln.end(), lns.begin(), lns.end());
+            for(auto &l : lns) infos[i].jmp[l] = 1;
+        }
+        // bfs
+        auto forward = infos, back = infos+1;
+        while(forward->ln.size() && back->ln.size()){
+            if(forward->ln.size() > back->ln.size())
+                swap(forward, back);
+            print("q[", back-infos, "] = ", back->ln, "\n")
+            int jump = bfs(*forward, back->jmp);
+            if( jump > 0 ) return jump;
+        }
+        return -1;
+    }
+    int bfs(SearchInfo & forward, map_t<int,int> & backJmp){
+        print("q[", &forward-infos, "] = ", forward.ln, "\n")
+        int ln = forward.ln.front(); forward.ln.pop_front();
+        int jmp = forward.jmp[ln];
+        print("m[", &forward-infos, "] = ", forward.jmp,"\n")
+        print("m[",infos-&forward+1,"] = ", backJmp,"\n")
+        for(auto &p : l2p[ln]){
+            print(p, ":->", p2l[p], "\n")
+            for(auto &l : p2l[p]){
+                if(l == ln || forward.jmp.count(l)) continue;
+                if(backJmp.count(l)) return jmp + backJmp[l];
+                forward.ln.push_back(l);
+                forward.jmp[l] = jmp + 1;
+            }
+        }
+        return -1;
+    }
+};
\ No newline at end of file