diff --git a/src/problem1.js b/src/problem1.js
index 9a14f2c..c46cb16 100644
--- a/src/problem1.js
+++ b/src/problem1.js
@@ -1,6 +1,30 @@
 function problem1(pobi, crong) {
-  var answer;
-  return answer;
+  if (pobi[1] - pobi[0] !== 1 || crong[1] - crong[0] !== 1) {
+    return -1;
+  }
+  const pobiMax = Math.max(maxValue(String(pobi[0])), maxValue(String(pobi[1])));
+  const crongMax = Math.max(maxValue(String(crong[0])), maxValue(String(crong[1])));
+
+  if(pobiMax > crongMax){
+    return 1;
+  } else if(pobiMax < crongMax){
+    return 2;
+  } else {
+    return 0;
+  }
+  
+}
+
+function maxValue(page){
+  let sum = 0;
+  let mul = 1;
+  const pageStr = page.split("");
+  for(let i of pageStr){
+    sum += Number(i);
+    mul *= Number(i);
+  }
+  return Math.max(sum, mul);
 }
 
+  
 module.exports = problem1;
diff --git a/src/problem2.js b/src/problem2.js
index cebd07c..31646dd 100644
--- a/src/problem2.js
+++ b/src/problem2.js
@@ -1,6 +1,14 @@
 function problem2(cryptogram) {
-  var answer;
-  return answer;
+  const stack = [];
+  let secret = cryptogram.split("");
+  for( let i = 0; i < secret.length; i++){
+    stack.push(secret[i]);
+    if(stack.length >= 2 && stack[stack.length - 1] === stack[stack.length - 2]){
+      stack.pop();
+      stack.pop();
+    }
+  }
+  return stack.join("");
 }
 
 module.exports = problem2;
diff --git a/src/problem3.js b/src/problem3.js
index 1baed28..512f39f 100644
--- a/src/problem3.js
+++ b/src/problem3.js
@@ -1,6 +1,14 @@
 function problem3(number) {
-  var answer;
-  return answer;
+  let clap = 0;
+  for(let i=1; i<=number; i++){
+    let str = String(i).split("");
+    for(let j of str){
+      if(j === "3" || j === "6" || j === "9"){
+        clap+=1;
+      }
+    }
+  }
+  return clap;
 }
 
 module.exports = problem3;
diff --git a/src/problem4.js b/src/problem4.js
index ee1d3bd..a1f5f3f 100644
--- a/src/problem4.js
+++ b/src/problem4.js
@@ -1,6 +1,24 @@
 function problem4(word) {
-  var answer;
-  return answer;
+  let result = '';
+
+  for (let i = 0; i < word.length; i++) {
+    const char = word[i];
+    const charCode = char.charCodeAt(0);
+
+    if (charCode >= 65 && charCode <= 90) {
+      const newCharCode = 90 + 65 - charCode;
+      result += String.fromCharCode(newCharCode);
+    } 
+    else if (charCode >= 97 && charCode <= 122) {
+      const newCharCode = 122 + 97 - charCode;
+      result += String.fromCharCode(newCharCode);
+    } 
+    else {
+      result += char;
+    }
+  }
+  return result;
 }
 
+
 module.exports = problem4;
diff --git a/src/problem5.js b/src/problem5.js
index 9368e87..28ff163 100644
--- a/src/problem5.js
+++ b/src/problem5.js
@@ -1,5 +1,12 @@
 function problem5(money) {
-  var answer;
+  const change = [50000, 10000, 5000, 1000, 500, 100, 50, 10, 1];
+  let answer = Array(change.length).fill(0);
+  let i = 0;
+  while(money !== 0){
+    answer[i] = parseInt(money/change[i]);
+    money = money % change[i];
+    i++;
+  }
   return answer;
 }
 
diff --git a/src/problem6.js b/src/problem6.js
index 3f842b5..e314aca 100644
--- a/src/problem6.js
+++ b/src/problem6.js
@@ -1,6 +1,26 @@
 function problem6(forms) {
-  var answer;
-  return answer;
+  let errorEmail = [];
+
+  for(let i=0;i<forms.length;i++){
+    const [email1, name1] = forms[i];
+    for(let j=i+1;j<forms.length;j++){
+      const [email2, name2] = forms[j];
+      for(let k=0;k<name1.length-1;k++){
+        const compareWords = name1.substring(k, k+2);
+        if(name2.includes(compareWords)){
+          if(!errorEmail.includes(email1)){
+            errorEmail.push(email1);
+          }
+          if(!errorEmail.includes(email2)){
+            errorEmail.push(email2);
+          }
+          break;
+        }
+      }
+    }
+  }
+
+  return errorEmail.sort();
 }
 
 module.exports = problem6;
diff --git a/src/problem7.js b/src/problem7.js
index ee1bb9d..970ce6d 100644
--- a/src/problem7.js
+++ b/src/problem7.js
@@ -1,6 +1,57 @@
 function problem7(user, friends, visitors) {
-  var answer;
-  return answer;
+  const friendMap = new Map();
+  const scoreMap = new Map();
+  const myFriends = new Set();
+
+  function addFriendship(a, b) {
+    if (!friendMap.has(a)) friendMap.set(a, new Set());
+    friendMap.get(a).add(b);
+  }
+
+  for (const [idA, idB] of friends) {
+    addFriendship(idA, idB);
+    addFriendship(idB, idA);
+
+    if (idA === user) myFriends.add(idB);
+    if (idB === user) myFriends.add(idA);
+  }
+
+  for (const visitorId of visitors) {
+    if (visitorId === user || myFriends.has(visitorId)) {
+      continue;
+    }
+
+    const currentScore = scoreMap.get(visitorId) || 0;
+    scoreMap.set(visitorId, currentScore + 1);
+  }
+
+  const userFriends = friendMap.get(user) || new Set();
+
+  for (const friendId of userFriends) {
+    const potentialFriends = friendMap.get(friendId) || new Set();
+
+    for (const candidateId of potentialFriends) {
+      if (candidateId === user || myFriends.has(candidateId)) {
+        continue;
+      }
+
+      const currentScore = scoreMap.get(candidateId) || 0;
+      scoreMap.set(candidateId, currentScore + 10);
+    }
+  }
+
+  const sortedCandidates = Array.from(scoreMap.entries())
+    .filter(([_, score]) => score > 0)
+    .sort(([idA, scoreA], [idB, scoreB]) => {
+      if (scoreA !== scoreB) {
+        return scoreB - scoreA;
+      }
+      return idA.localeCompare(idB);
+    })
+    .map(([id, _]) => id)
+    .slice(0, 5);
+
+  return sortedCandidates;
 }
 
 module.exports = problem7;