diff --git a/4. Combinatorial search/APSS_ALLERGY_minkyu.cpp b/4. Combinatorial search/APSS_ALLERGY_minkyu.cpp
new file mode 100644
index 0000000..6995c7d
--- /dev/null
+++ b/4. Combinatorial search/APSS_ALLERGY_minkyu.cpp	
@@ -0,0 +1,78 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+using matrix = vector<vector<int> >;
+int T, n, m;
+int MAX_DEPTH;
+// nameIndex[name] : table에서 해당 이름을 가진 사람의 행 번호 저장
+map<string, int> nameIndex;
+// foodEater[i] : i번째 음식을 먹을 수 있는 사람들의 리스트
+matrix foodEater;
+// eaterFood[i] : i번째 사람이 먹을 수 있는 음식 리스트
+matrix eaterFood;
+// 현재 상태
+vector<int> edible;
+
+int search(int start) {
+    return distance(edible.begin(), find(edible.begin(), edible.end(), 0));
+}
+
+void select(int food) {
+    for (int saram: foodEater[food]) {
+        edible[saram]++;
+    }
+}
+
+void unselect(int food) {
+    for (int saram: foodEater[food]) {
+        edible[saram]--;
+    }
+}
+
+// start 번 음식부터 시작
+void solve(int start, int num) {
+    if (num >= MAX_DEPTH) return;
+    if (find(edible.begin(), edible.end(), 0) == edible.end()) {
+        MAX_DEPTH = num;
+        return;
+    }
+    int inedible = search(start);
+    for (int food: eaterFood[inedible]) {
+        select(food);
+        solve(food+1, num+1);
+        unselect(food);
+    }
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+    cin >> T;
+    while(T--) {
+        MAX_DEPTH = 21;
+        cin >> n >> m;
+        foodEater = matrix(m);
+        eaterFood = matrix(n);
+        edible = vector<int>(n, 0);
+        for (int i = 0; i < n; i++) {
+            string name;
+            cin >> name;
+            nameIndex[name] = i;
+        }
+        for (int i = 0; i < m; i++) {
+            int num;
+            cin >> num;
+            while(num--) {
+                string name;
+                cin >> name;
+                int person = nameIndex[name];
+                foodEater[i].push_back(person);
+                eaterFood[person].push_back(i);
+            }
+        }
+        solve(0, 0);
+        cout << MAX_DEPTH << endl;
+    }
+}
\ No newline at end of file
diff --git "a/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/APSS_ARTIC_minkyu.cpp" "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/APSS_ARTIC_minkyu.cpp"
new file mode 100644
index 0000000..258c862
--- /dev/null
+++ "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/APSS_ARTIC_minkyu.cpp"	
@@ -0,0 +1,70 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+using matrix = vector<vector<double> >;
+
+struct Point {
+    double x, y;
+};
+
+int C, n;
+vector<Point> base;
+matrix dist;
+vector<bool> visited;
+vector<bool> decisioned;
+
+bool decision(int here, double gap) {
+    decisioned[here] = true;
+    visited[here] = true;
+    for (int i = 0; i < n; i++) {
+        if (dist[here][i] < gap) {
+            visited[i] = true;
+        }
+    }
+    if (find(visited.begin(), visited.end(), 0) != visited.end()) {
+        for (int i = 0; i < n; i++) {
+            if (visited[i] && !decisioned[i]) return decision(i, gap);
+        }
+        return false;
+    }
+    return true;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+    cout << fixed;
+    cout.precision(2);
+    cin >> C;
+    while(C--) {
+        cin >> n;
+        base = vector<Point>();
+        dist = matrix(n, vector<double>(n, 0));
+        for (int i = 0; i < n; i++) {
+            double x, y;
+            cin >> x >> y;
+            base.push_back(Point{x, y});
+        }
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < n; j++) {
+                if (i == j) continue;
+                double gap = pow(pow(abs(base[i].x-base[j].x), 2) + pow(abs(base[i].y-base[j].y), 2), 0.5);
+                dist[i][j] = gap;
+                dist[j][i] = gap;
+            }
+        }
+
+        double lo = 0, hi = 2e6+1;
+        double mid;
+        for (int i = 0; i < 100; i++) {
+            visited = vector<bool>(n, 0);
+            decisioned = vector<bool>(n, 0);
+            mid = (lo + hi) / 2.0;
+            if (decision(0, mid)) hi = mid;
+            else lo = mid;
+        }
+        cout << mid << endl;
+    }
+}
\ No newline at end of file
diff --git "a/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/APSS_DARPA_minkyu.cpp" "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/APSS_DARPA_minkyu.cpp"
new file mode 100644
index 0000000..f92033b
--- /dev/null
+++ "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/APSS_DARPA_minkyu.cpp"	
@@ -0,0 +1,44 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+
+int C, N, M;
+vector<double> settable;
+
+bool decision(int cameras, double gap) {
+    double limit = -1;
+    int installed = 0;
+    for (int i = 0; i < settable.size(); i++) {
+        if (limit <= settable[i]) {
+            installed++;
+            limit = settable[i] + gap;
+        }
+    }
+    return installed >= cameras;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+    cin >> C;
+    cout << fixed;
+    cout.precision(2);
+    while (C--) {
+        cin >> N >> M;
+        settable = vector<double>(M);
+        for (int i = 0; i < M; i++) {
+            cin >> settable[i];
+        }
+        cout << endl;
+        double lo = 0, hi = 241;
+        double mid;
+        for (int i = 0; i < 100; i++) {
+            mid = (lo + hi) / 2.0;
+            if(decision(N, mid)) lo = mid;
+            else hi = mid;
+        }
+        cout << lo << endl;
+    }
+}
\ No newline at end of file
diff --git "a/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1477_minkyu.cpp" "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1477_minkyu.cpp"
new file mode 100644
index 0000000..3a1f75e
--- /dev/null
+++ "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1477_minkyu.cpp"	
@@ -0,0 +1,49 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+
+int N, M, L;
+vector<int> station;
+vector<int> distances;
+
+// 모든 간격이 low 이상으로 가능?
+bool decision(double low) {
+    int howmany = 0;
+    for (int d: distances) {
+        howmany += ceil(d / low)-1;
+    }
+    return howmany <= M;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+    
+    cin >> N >> M >> L;
+    if (N == 0) {
+        cout << ceil(L/(double)(M+1)) << endl;
+        return 0;
+    }
+    station = vector<int>(N);
+    distances = vector<int>(N+1);
+    for (int i = 0; i < N; i++) cin >> station[i];
+    sort(station.begin(), station.end());
+    distances[0] = station[0];
+    for (int i = 1; i < N; i++) {
+        distances[i] = station[i] - station[i-1];
+    }
+    distances[N] = L - station[N-1];
+
+    double lo = -1, hi = 2001;
+    double mid;
+    for (int i = 0; i < 100; i++) {
+        mid = (lo + hi) / 2;
+        if (decision(mid)) hi = mid;
+        else lo = mid;
+    }
+    
+    // 반드시 올림 해야됨
+    cout << ceil(mid) << endl;
+}
\ No newline at end of file
diff --git "a/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1561_minkyu.cpp" "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1561_minkyu.cpp"
new file mode 100644
index 0000000..4d2ce2b
--- /dev/null
+++ "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1561_minkyu.cpp"	
@@ -0,0 +1,54 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+
+int N, M;
+vector<long long> rides;
+
+bool decision(long long n) {
+    long long ret = 0;
+    for (int i = 1; i <= M; i++) {
+        ret += ceil(n / (double)rides[i]);
+    }
+    return ret >= N;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+
+    cin >> N >> M;
+    rides = vector<long long>(M+1);
+    for (int i = 1; i <= M; i++) cin >> rides[i];
+
+    if (M >= N) {
+        cout << N;
+        return 0;
+    }
+
+    // 아래 for문이 끝나면 모든 아이들이 빠짐없이 놀이기구를 타는데 hi분이 걸리는 것을 알 수 있음
+    long long lo = 0;
+    long long hi = 1e15;
+    long long mid;
+    for (int i = 0; i < 100; i++) {
+        mid = (lo + hi) / 2;
+        if (decision(mid)) hi = mid;
+        else lo = mid;
+    }
+
+    // 이제 hi분을 기준으로 가장 마지막에 탄 놀이기구가 무엇인지 찾으면 됨
+    long long child = 0;
+    for (int i = 1; i <= M; i++) {
+        child += ceil(mid / (double)rides[i]);
+    }
+    for (int i = 1; i <= M; i++) {
+        if (mid % rides[i] == 0) {
+            if (++child == N) {
+                cout << i << endl;
+                return 0;
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git "a/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1939_minkyu.cpp" "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1939_minkyu.cpp"
new file mode 100644
index 0000000..187a7d1
--- /dev/null
+++ "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_1939_minkyu.cpp"	
@@ -0,0 +1,51 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+using matrix = vector<map<int, int> >;
+
+int N, M;
+int A, B, C;
+matrix bridge;
+int f1, f2;
+
+bool DFS(int start, int weight, vector<bool>& visited) {
+    if (start == f2) return true;
+    visited[start] = true;
+
+    bool ret = false;
+    for (pair<int, int> next: bridge[start]) {
+        if (!visited[next.first] && next.second >= weight) ret = DFS(next.first, weight, visited);
+        if (ret) return true;
+    }
+
+    return false;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+
+    cin >> N >> M;
+    bridge = matrix(N+1);
+
+    for (int i = 0; i < M; i++) {
+        cin >> A >> B >> C;
+        int& temp = bridge[A][B];
+        temp = max(temp, C);
+        bridge[B][A] = temp;
+    }
+    cin >> f1 >> f2;
+    
+
+    int lo = -1, hi = 1e9+1;
+    int mid;
+    for (int i = 0; i < 100; i++) {
+        mid = (lo + hi) / 2;
+        vector<bool> visited (N+1, false);
+        if(DFS(f1, mid, visited)) lo = mid;
+        else hi = mid;
+    }
+    cout << mid << endl;
+}
\ No newline at end of file
diff --git "a/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_2470_minkyu.cpp" "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_2470_minkyu.cpp"
new file mode 100644
index 0000000..e584669
--- /dev/null
+++ "b/5. \354\265\234\354\240\201\355\231\224 \352\262\260\354\240\225 \353\254\270\354\240\234/BJ_2470_minkyu.cpp"	
@@ -0,0 +1,51 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+
+int N;
+vector<int> liquid;
+
+bool decision(int sum) {
+
+    return true;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+    
+    cin >> N;
+    liquid = vector<int>(N);
+    for (int i = 0; i < N; i++) cin >> liquid[i];
+
+    sort(liquid.begin(), liquid.end());
+    
+    vector<int>::iterator i = liquid.begin(), j = liquid.end()-1;
+    vector<int>::iterator left = liquid.begin(), right = liquid.end()-1;
+    int gap = *i + *j;
+    int mingap = abs(gap);
+    while (i < j-1) {
+        if (gap > 0) {
+            j--;
+            gap = *i + *j;
+            if (mingap > abs(gap)) {
+                mingap = abs(gap);
+                left = i;
+                right = j;
+            }
+        }
+        else if (gap < 0) {
+            i++;
+            gap = *i + *j;
+            if (mingap > abs(gap)) {
+                mingap = abs(gap);
+                left = i;
+                right = j;
+            }
+        }
+        else break;
+    }
+    cout << *left << ' ' << *right << endl;
+}
\ No newline at end of file
diff --git a/6. BFS, DFS/APSS_DICTIONARY_minkyu.cpp b/6. BFS, DFS/APSS_DICTIONARY_minkyu.cpp
new file mode 100644
index 0000000..b837a02
--- /dev/null
+++ b/6. BFS, DFS/APSS_DICTIONARY_minkyu.cpp	
@@ -0,0 +1,90 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+
+int C, N;
+vector<list<int> > G;
+vector<int> inorder;
+list<char> result;
+int numAlpha;
+
+int pop(list<int>& q) {
+    int ret = q.back();
+    q.pop_back();
+    return ret;
+}
+
+bool toplogical() {
+    list<int> q;
+    for (int i = 0; i < 26; i++) {
+        if (inorder[i] == 0) q.push_back(i);
+    }
+    while(q.size() > 0) {
+        int here = pop(q);
+        for (int there: G[here]) {
+            if(--inorder[there] == 0) q.push_back(there);
+        }
+        result.push_back(here+'a');
+        --numAlpha;
+    }
+    return numAlpha == 0;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+
+    cin >> C;
+    while (C--) {
+        G = vector<list<int> >(26);
+        inorder = vector<int>(26, -1);
+        result.clear();
+        numAlpha = 0;
+
+        cin >> N;
+        string before;
+        string now;
+        cin >> before;
+
+        while (--N) {
+            cin >> now;
+            int size = min(before.size(), now.size());
+            for (int i = 0; i < size; i++) {
+                if (before[i] != now[i]) {
+                    int from = before[i] - 'a';
+                    int to = now[i] - 'a';
+                    G[from].push_back(to);
+                    if (inorder[from] < 0) inorder[from] = 0;
+                    if (inorder[to] < 0) {
+                        inorder[to] = 1;
+                    }
+                    else ++inorder[to];
+                    break;
+                }
+            }
+            before = now;
+        }
+
+        for (int i = 0; i < 26; ++i) {
+            if (inorder[i] < 0) {
+                result.push_back(i+'a');
+                continue;
+            }
+            ++numAlpha;
+        }
+
+        bool valid = toplogical();
+
+        if (valid) {
+            for (char c: result) cout << c;
+            cout << endl;
+            continue;
+        } else {
+            cout << "INVALID HYPOTHESIS" << endl;
+            continue;
+        }
+        
+    }    
+}
\ No newline at end of file
diff --git a/6. BFS, DFS/BJ_2021_minkyu.cpp b/6. BFS, DFS/BJ_2021_minkyu.cpp
new file mode 100644
index 0000000..f4fc1fb
--- /dev/null
+++ b/6. BFS, DFS/BJ_2021_minkyu.cpp	
@@ -0,0 +1,76 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+int N, L, src, dst;
+vector<list<int> > hosun;
+vector<list<int> > jiha;
+vector<bool> hosunSeen;
+vector<bool> jihaSeen;
+
+int pop(vector<int>& q) {
+    int ret = q.back();
+    q.pop_back();
+    return ret;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+    cin >> N >> L;
+    hosun = vector<list<int> >(L+1);
+    hosunSeen = vector<bool>(L+1, false);
+    jiha = vector<list<int> >(N+1);
+    jihaSeen = vector<bool>(N+1, false);
+
+    for (int i = 0; i < L; ++i) {
+        int j;
+        cin >> j;
+        while(j > 0) {
+            hosun[i].push_back(j);
+            jiha[j].push_back(i);
+            cin >> j;
+        }
+    }
+
+    cin >> src >> dst;
+
+    int here = src;
+    vector<int> q1;
+    vector<int> q2;
+    int minimumTransfer = 0;
+
+    for(int e: jiha[here]) {
+        q1.push_back(e);
+    }
+
+    for (; ; ++minimumTransfer) {
+        if (q1.empty()) {
+            cout << -1 << endl;
+            return 0;
+        }
+        while(!q1.empty()) {
+            int hosun_num = pop(q1);
+            if (hosunSeen[hosun_num]) continue;
+            for (int jiha_num: hosun[hosun_num]) {
+                if (jihaSeen[jiha_num]) continue;
+                if (jiha_num == dst) goto FINISH;
+                q2.push_back(jiha_num);
+            }
+            hosunSeen[hosun_num] = true;
+        }
+        while(!q2.empty()) {
+            here = pop(q2);
+            if (jihaSeen[here]) continue;
+            for(int e: jiha[here]) {
+                if (hosunSeen[e]) continue;
+                q1.push_back(e);
+            }
+            jihaSeen[here] = true;
+        }
+    }
+    FINISH:
+    cout << minimumTransfer << endl;
+    return 0;
+}
\ No newline at end of file
diff --git a/6. BFS, DFS/BJ_3584_minkyu.cpp b/6. BFS, DFS/BJ_3584_minkyu.cpp
new file mode 100644
index 0000000..d06ea76
--- /dev/null
+++ b/6. BFS, DFS/BJ_3584_minkyu.cpp	
@@ -0,0 +1,48 @@
+#include <bits/stdc++.h>
+#define endl '\n'
+
+using namespace std;
+
+int T, N;
+vector<int> parentOf;
+vector<bool> seen;
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+    cin >> T;
+    while(T--) {
+        cin>> N;
+        parentOf = vector<int>(N+1, 0);
+        seen = vector<bool>(N+1, false);
+        int parent, child;
+        for (int i = 1; i < N; ++i) {
+            cin >> parent >> child;
+            parentOf[child] = parent;
+        }
+        int A, B;
+        cin >> A >> B;
+        parent = A;
+        while (parent) {
+            if (parent == B) {
+                cout << parent << endl;
+                goto FINISH;
+            }
+            seen[parent] = true;
+            parent = parentOf[parent];
+        }
+
+        parent = B;
+        while(parent) {
+            if (seen[parent]) {
+                cout << parent << endl;
+                goto FINISH;
+            }
+            parent = parentOf[parent];
+        }
+
+        FINISH:
+        continue;
+    }
+}
\ No newline at end of file