diff --git a/src/problem1.js b/src/problem1.js
index 9a14f2c..728e8c7 100644
--- a/src/problem1.js
+++ b/src/problem1.js
@@ -1,6 +1,36 @@
 function problem1(pobi, crong) {
-  var answer;
-  return answer;
+  if (pobi[1] !== pobi[0]+1 || crong[1] !== crong[0]+1){
+    return -1;
+  }
+
+  const pobiValue = Math.max(getMaxValue(pobi[0]), getMaxValue(pobi[1]));
+  const crongValue = Math.max(getMaxValue(crong[0]), getMaxValue(crong[1]));
+
+  if (pobiValue > crongValue) {
+    return 1;
+  } 
+
+  else if (pobiValue < crongValue) {
+    return 2;
+  } 
+  
+  else {
+    return 0;
+  }
+}
+
+function getMaxValue(page) {
+  let sum = 0;
+  let mul = 1;
+
+  const numbers = String(page).split("");
+
+  for (let number of numbers) {
+    sum += Number(number);
+    mul *= Number(number);
+  }
+
+  return Math.max(sum, mul);
 }
 
 module.exports = problem1;
diff --git a/src/problem2.js b/src/problem2.js
index cebd07c..86a2ecf 100644
--- a/src/problem2.js
+++ b/src/problem2.js
@@ -1,6 +1,19 @@
 function problem2(cryptogram) {
-  var answer;
-  return answer;
+  const stack = [];
+
+  for (let i = 0; i < cryptogram.length; i++) {
+    const char = cryptogram[i];
+
+    if (stack[stack.length-1] === char){
+      stack.pop();
+    } 
+    
+    else {
+      stack.push(char);
+    }
+  }
+
+  return stack.join("")
 }
 
 module.exports = problem2;
diff --git a/src/problem3.js b/src/problem3.js
index 1baed28..0226c44 100644
--- a/src/problem3.js
+++ b/src/problem3.js
@@ -1,6 +1,15 @@
 function problem3(number) {
-  var answer;
-  return answer;
+  let count = 0;
+
+  for (let num = 1; num <= number; num++) {
+    const str = num.toString();
+
+    if (str.match(/[369]/g)){
+      count += str.match(/[369]/g).length;
+    }
+  }
+
+  return count;
 }
 
 module.exports = problem3;
diff --git a/src/problem4.js b/src/problem4.js
index ee1d3bd..dd92440 100644
--- a/src/problem4.js
+++ b/src/problem4.js
@@ -1,6 +1,31 @@
 function problem4(word) {
-  var answer;
-  return answer;
+  const dict = new Map();
+
+  for (let i = 0; i < 26; i++) {
+    const upper = String.fromCharCode(65+i);
+    const reverseUpper = String.fromCharCode(90-i);
+    dict.set(upper, reverseUpper);
+  }
+
+  for (let i = 0; i < 26; i++) {
+    const lower = String.fromCharCode(97+i);
+    const reverseLower = String.fromCharCode(122-i);
+    dict.set(lower, reverseLower);
+  }
+
+  let result = "";
+
+  for (const char of word) {
+    if (dict.has(char)) {
+      result += dict.get(char);
+    } 
+
+    else {
+      result += char;
+    }
+  }
+  
+  return result;
 }
 
 module.exports = problem4;
diff --git a/src/problem5.js b/src/problem5.js
index 9368e87..4bd5195 100644
--- a/src/problem5.js
+++ b/src/problem5.js
@@ -1,6 +1,13 @@
 function problem5(money) {
-  var answer;
-  return answer;
+  const moneyUnit= [50000, 10000, 5000, 1000, 500, 100, 50, 10, 1];
+  const result = [];
+
+  moneyUnit.forEach(unit => {
+    result.push(Math.floor(money/unit));
+    money %= unit; 
+  });
+  
+  return result;
 }
 
 module.exports = problem5;
diff --git a/src/problem6.js b/src/problem6.js
index 3f842b5..b0c3cb7 100644
--- a/src/problem6.js
+++ b/src/problem6.js
@@ -1,6 +1,20 @@
 function problem6(forms) {
-  var answer;
-  return answer;
+  const result = new Set();
+
+  for (let i = 0; i < forms.length; i++) {
+    for (let j = i+1; j < forms.length; j++) {
+      for (let k = 0; k < forms[i][1].length-1; k++) {
+        const piece = forms[i][1].slice(k, k+2);
+
+        if (forms[j][1].includes(piece)) {
+          result.add(forms[i][0]);
+          result.add(forms[j][0]);
+        }
+      }
+    }
+  }
+
+  return Array.from(result).sort()
 }
 
 module.exports = problem6;
diff --git a/src/problem7.js b/src/problem7.js
index ee1bb9d..2abf8bd 100644
--- a/src/problem7.js
+++ b/src/problem7.js
@@ -1,6 +1,54 @@
 function problem7(user, friends, visitors) {
-  var answer;
-  return answer;
+  const friendList = new Set();
+  const score = new Map();
+
+  for (const [friend1, friend2] of friends) {
+    if (friend1 === user) {
+      friendList.add(friend2);
+    }
+    else if (friend2 === user) {
+      friendList.add(friend1);
+    }
+  }
+
+  for (const [friend1, friend2] of friends) {
+    if (friend1 !== user && friend2 !== user) {
+      if (friendList.has(friend1)) {
+        score.set(friend2, (score.get(friend2) || 0)+10);
+      }
+
+      if (friendList.has(friend2)) {
+        score.set(friend1, (score.get(friend1) || 0)+10);
+      }
+    }
+  }
+
+  for (const visitor of visitors) {
+    if (!friendList.has(visitor) && visitor !== user) {
+      score.set(visitor, (score.get(visitor) || 0)+1);
+    }
+  }
+
+  const sorted = Array.from(score).sort((a, b) => {
+    if (b[1] !== a[1]) {
+      return b[1]-a[1];
+    }
+
+    return a[0].localeCompare(b[0]);
+  });
+
+  const result = [];
+  for (const [name, score_] of sorted) {
+    if (result.length === 5) {
+      break;
+    }
+
+    if (score_ > 0) {
+      result.push(name);
+    }
+  }
+
+  return result;
 }
 
 module.exports = problem7;