diff --git a/10448.cpp b/10448.cpp
new file mode 100644
index 0000000..2dc6b6b
--- /dev/null
+++ b/10448.cpp
@@ -0,0 +1,37 @@
+//
+// Created by LG on 2021-09-26.
+//
+#include <iostream>
+
+using namespace std;
+
+int triangle(int t, int* tri){
+
+    for(int i=0; i<45; i++){
+        for(int j=0; j<45; j++){
+            for(int k=0; k<45; k++){
+                if(tri[i] + tri[j] + tri[k] == t)
+                    return 1;
+            }
+        }
+    }
+    return 0;
+}
+
+int main(){
+    int n;
+    cin >> n;
+
+    int start = 1;
+    int tri[45];
+    for(int i=2; i<47; i++){
+        tri[i-2] = start;
+        start += i;
+    }
+
+    for(int i=0; i<n; i++){
+        int t;
+        cin >> t;
+        cout << triangle(t, tri) << '\n';
+    }
+}
diff --git a/20055.cpp b/20055.cpp
new file mode 100644
index 0000000..eaecf41
--- /dev/null
+++ b/20055.cpp
@@ -0,0 +1,99 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+void moveBelt(vector<int> &durab, int &up, int &down, int n){
+    if(up == 0)
+        up = 2*n-1;
+    else
+        up--;
+    if(down == 0)
+        down = 2*n-1;
+    else
+        down--;
+}
+
+void moveRobot(vector<int> &durab, int up, int down, vector<bool> &robot, int n){
+    if(down>up){
+        for(int i=down-1; i>up; i--){
+            if(durab[i+1] > 0 && robot[i] && !robot[i+1]){
+                robot[i] = false;
+                robot[i+1] = true;
+                durab[i+1]--;
+            }
+            robot[down] = false;
+        }
+    }
+    else if(down<up){
+        for(int i=down-1; i>=0; i--){
+            if(durab[i+1] > 0 && robot[i] && !robot[i+1]){
+                robot[i] = false;
+                robot[i+1] = true;
+                durab[i+1]--;
+            }
+            robot[down] = false;
+        }
+        for(int i=2*n-1; i>up; i--){
+            if(i==2*n-1){
+                if(durab[0] > 0 && robot[i] && !robot[0]){
+                    robot[i] = false;
+                    robot[0] = true;
+                    durab[0]--;
+                }
+            }
+            else if(durab[i+1] > 0 && robot[i] && !robot[i+1]){
+                robot[i] = false;
+                robot[i+1] = true;
+                durab[i+1]--;
+            }
+            robot[down] = false;
+        }
+    }
+}
+
+int main(){
+    int n, k, count = 1;
+    cin >> n >> k;
+
+    int up = 0, down = n-1;
+    vector<bool> robot(2*n, false); //로봇 유무
+    vector<int> durab(2*n, 0); //내구도
+
+    //입력
+    for(int i=0; i<2*n; i++){
+        cin >> durab[i];
+    }
+
+    while(true){
+        //1. 내리는 위치와 올리는 위치 옮김
+        moveBelt(durab, up, down, n);
+        robot[down] = false; //내리는 위치 로봇 바로 내림.
+
+        //2. 이동 가능한 로봇을 이동.
+        moveRobot(durab, up, down, robot, n);
+
+        //3. 올리는 위치에 올림
+        if(durab[up] != 0){
+            robot[up] = true;
+            durab[up]--;
+        }
+
+        //4. 내구도 0인 칸 세기
+        int zero = 0;
+        for(int i=0; i<2*n; i++){
+            if(durab[i] <= 0){
+                zero++;
+            }
+        }
+
+        //종료 조건
+        if(zero >= k){
+            cout << count;
+            break;
+        }
+
+        count++;
+    }
+
+}
\ No newline at end of file
diff --git a/2108.cpp b/2108.cpp
new file mode 100644
index 0000000..114e597
--- /dev/null
+++ b/2108.cpp
@@ -0,0 +1,50 @@
+#include <iostream>
+#include <algorithm>
+#include <cmath>
+
+using namespace std;
+
+int main(){
+    int n;
+    cin >> n;
+
+    double sum = 0; //float은 틀린다.
+    int max = -4000, min = 4000;
+    int mid[n];
+    int mode[8001] = {0, };
+
+    for(int i=0; i<n; i++){
+        int t;
+        cin >> t;
+        sum += t;
+        if(t > max)
+            max = t;
+        if(t < min)
+            min = t;
+        mid[i] = t;
+        mode[t+4000]++;
+    }
+
+    cout << round(double(sum/n)) << '\n';
+
+    sort(mid, mid+n);
+    cout << mid[n/2] << '\n';
+
+    int k = -1;
+    int index = 0, count = 0;
+    for(int i=0; i<8001; i++){
+        if(mode[i] > k){
+            k = mode[i];
+            index = i;
+            count = 0;
+        }
+        else if(mode[i] == k && count<1){
+            count++;
+            index = i;
+        }
+    }
+    cout << index-4000 << '\n';
+
+    cout << max-min;
+
+}
diff --git a/2858.cpp b/2858.cpp
new file mode 100644
index 0000000..7bb2dd3
--- /dev/null
+++ b/2858.cpp
@@ -0,0 +1,22 @@
+#include <iostream>
+
+using namespace std;
+
+int main() {
+    int r, b;
+    cin >> r >> b;
+    int area = r + b;
+
+    int w=0, l=0;
+    for(int i=1; i<area/2; i++){
+        if(area%i == 0){
+            w = i;
+            l = area/i;
+        }
+        int temp = (w-1)*2+(l-1)*2;
+        if(temp == r && area-temp == b){
+            cout << max(w, l) << ' ' << min(w, l);
+            break;
+        }
+    }
+}
diff --git a/3077.cpp b/3077.cpp
new file mode 100644
index 0000000..45d1b6f
--- /dev/null
+++ b/3077.cpp
@@ -0,0 +1,39 @@
+//
+// Created by LG on 2021-09-27.
+//
+#include <iostream>
+#include <map>
+#include <vector>
+
+using namespace std;
+
+int score(int n, map<string, int> answer, vector<string> hyunwoo){
+    int count = 0;
+    for(int i=0; i<n; i++){
+        for(int j=i+1; j<n; j++){
+            if(answer[hyunwoo[i]] < answer[hyunwoo[j]]){
+                count++;
+            }
+        }
+    }
+    return count;
+}
+
+int main(){
+    int n;
+    cin >> n;
+
+    map<string, int> answer;
+    for(int i=0; i<n; i++){
+        string s;
+        cin >> s;
+        answer.insert(pair<string, int>(s, i));
+    }
+
+    vector<string> hyunwoo(n);
+    for(int i=0; i<n; i++){
+        cin >> hyunwoo[i];
+    }
+
+    cout << score(n, answer, hyunwoo) << "/" << n*(n-1)/2;
+}
\ No newline at end of file