diff --git a/.idea/gradle.xml b/.idea/gradle.xml
new file mode 100644
index 0000000..2a65317
--- /dev/null
+++ b/.idea/gradle.xml
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="GradleMigrationSettings" migrationVersion="1" />
+  <component name="GradleSettings">
+    <option name="linkedExternalProjectsSettings">
+      <GradleProjectSettings>
+        <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleHome" value="" />
+        <option name="modules">
+          <set>
+            <option value="$PROJECT_DIR$" />
+          </set>
+        </option>
+      </GradleProjectSettings>
+    </option>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
new file mode 100644
index 0000000..5d98256
--- /dev/null
+++ b/.idea/misc.xml
@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="FrameworkDetectionExcludesConfiguration">
+    <file type="web" url="file://$PROJECT_DIR$" />
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_11" default="true" project-jdk-name="11" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 0000000..94a25f7
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/src/main/java/org/example/Collatz.java b/src/main/java/org/example/Collatz.java
new file mode 100644
index 0000000..d93f84c
--- /dev/null
+++ b/src/main/java/org/example/Collatz.java
@@ -0,0 +1,24 @@
+package org.example;
+
+public class Collatz {
+    public int solution(long num) {
+        int cnt =1;
+        if(num == 1){
+            return 0;
+        }
+        while(cnt<=500){
+            if(num%2==0){
+                num /=2;
+            }else{
+                num *= 3;
+                num += 1;
+            }
+            if(num ==1){
+                return cnt;
+            }
+            cnt ++;
+        }
+
+        return -1;
+    }
+}
diff --git a/src/main/java/org/example/sol2.java b/src/main/java/org/example/sol2.java
new file mode 100644
index 0000000..7eb4ea9
--- /dev/null
+++ b/src/main/java/org/example/sol2.java
@@ -0,0 +1,13 @@
+package org.example;
+
+public class sol2 {
+    public int solution(int n) {
+        int answer = 0;
+        while(n>0){
+            answer += (n%10);
+            n /= 10;
+        }
+
+        return answer;
+    }
+}
diff --git a/src/main/java/org/example/sol3.java b/src/main/java/org/example/sol3.java
new file mode 100644
index 0000000..61870e2
--- /dev/null
+++ b/src/main/java/org/example/sol3.java
@@ -0,0 +1,23 @@
+package org.example;
+
+public class sol3 {
+    boolean solution(String s) {
+        int pcnt =0;
+        int ycnt =0;
+        String small = s.toLowerCase();
+        for(char c: small.toCharArray()){
+            if(c=='p'){
+                pcnt++;
+            }else if(c=='y'){
+                ycnt++;
+            }
+        }
+        if(pcnt==ycnt){
+            return true;
+        }else{
+            return false;
+        }
+    }
+}
+
+// s문자열 다 소문자로 바꾸고 foreach로 p와 y개수 세고 리턴해준다
diff --git a/src/main/java/org/example/sol4.java b/src/main/java/org/example/sol4.java
new file mode 100644
index 0000000..143e242
--- /dev/null
+++ b/src/main/java/org/example/sol4.java
@@ -0,0 +1,14 @@
+package org.example;
+
+public class sol4 {
+    public int solution(int n) {
+        int answer = 0;
+        for(int i =1; i<n; i++){
+            if(n%i==1){
+                answer = i;
+                break;
+            }
+        }
+        return answer;
+    }
+}
diff --git a/src/main/java/org/example/sol5.java b/src/main/java/org/example/sol5.java
new file mode 100644
index 0000000..3363941
--- /dev/null
+++ b/src/main/java/org/example/sol5.java
@@ -0,0 +1,17 @@
+package org.example;
+
+public class sol5 {
+    public boolean solution(String s) {
+        boolean answer = true;
+        if(s.length()==4||s.length()==6){
+            for(char c: s.toCharArray()){
+                if((int)c>=97&&(int)c<=122 || (int)c>=65 && (int)c<=90){
+                    answer = false;
+                }
+            }
+        }else{
+            answer =false;
+        }
+        return answer;
+    }
+}
diff --git a/src/main/java/org/example/sol6.java b/src/main/java/org/example/sol6.java
new file mode 100644
index 0000000..76f7592
--- /dev/null
+++ b/src/main/java/org/example/sol6.java
@@ -0,0 +1,20 @@
+package org.example;
+
+public class sol6 {
+    public boolean solution(int x) {
+        int n = x;
+        int j =10;
+        int sum = 0;
+        while(n >0){
+            int i=0;
+            i = n%j;
+            n /=j;
+            sum += i;
+        }
+        if(x % sum ==0){
+            return true;
+        }else{
+            return false;
+        }
+    }
+}
diff --git a/src/main/java/org/example/sol7.java b/src/main/java/org/example/sol7.java
new file mode 100644
index 0000000..240a240
--- /dev/null
+++ b/src/main/java/org/example/sol7.java
@@ -0,0 +1,14 @@
+package org.example;
+
+public class sol7 {
+    public String solution(String[] seoul) {
+    String location;
+    for(int i=0; i<seoul.length; i++){
+        if(seoul[i].equals("Kim")){
+            location = Integer.toString(i);
+            return "김서방은 "+location+"에 있다";
+        }
+    }
+    return "kim 없음";
+}
+}
diff --git a/src/main/java/org/example/solution1.java b/src/main/java/org/example/solution1.java
index 16cd2d4..256a277 100644
--- a/src/main/java/org/example/solution1.java
+++ b/src/main/java/org/example/solution1.java
@@ -1,17 +1,20 @@
 package org.example;
 
 public class solution1 {
-    public double solution(int[] arr) {
-        double answer = 0;
-        double tot =0;
-        for(int i: arr){
-            tot += i;
+    public String solution(int num) {
+
+        StringBuilder sb = new StringBuilder();
+        if(num%2 ==0){
+            sb.append("Even");
+        }else{
+            sb.append("Odd");
         }
-        answer = tot/(arr.length);
-        return answer;
+        return sb.toString();
     }
 }
 
+// 스트링 빌더를 만들어서 num을 2로 나누었을 때 짝수라면 even추가 홀수라면 odd를 스트링 빌더에 추가함.
+
 
 // 주석에 쓸 내용 : 자신이 이 문제를 어떻게 풀었는지 쓰기, 어려워서 못 풀었으면 어떤 부분이 어려웠는지 남기기.
 // solution1에 첫문제 풀고 다음날 부터 솔루션2,3,4.. 클래스 만들어서 풀고 커밋하기