diff --git a/challenge-1/index.js b/challenge-1/index.js
new file mode 100644
index 0000000..066181f
--- /dev/null
+++ b/challenge-1/index.js
@@ -0,0 +1,18 @@
+var twoSum = function (nums, target) {
+    if (!Array.isArray(nums) || typeof target !== 'number') {
+        return 0;
+    }
+    let result = [];
+    let element = new Map();
+    for (let i = 0; i < nums.length; i++) {
+        let difference = target - nums[i];
+        if (element.has(difference)) {
+            result.push(nums.indexOf(difference), i);
+        }
+        else {
+            element.set(nums[i], true);
+        }
+    };
+    return result;
+}
+console.log(twoSum(nums,target))
\ No newline at end of file
diff --git a/challenge-2/index.js b/challenge-2/index.js
new file mode 100644
index 0000000..817e9bc
--- /dev/null
+++ b/challenge-2/index.js
@@ -0,0 +1,33 @@
+var maxProfit = function(prices) {
+    if(!Array.isArray(prices)){
+        return 0;
+    }
+    let left = 0;
+    let right = 1;
+    let difference = [];
+    findIndex(left,right,difference);
+    function findIndex(left,right,difference){
+       if(right==prices.length){
+        return;
+       }
+       else if(prices[left]<prices[right]){
+        let value = prices[right]-prices[left];
+        difference.push(value);
+        right++;
+        return findIndex(left,right,difference)
+       }
+       else if(prices[right]<=prices[left]){
+        left=right;
+        right++;
+        return findIndex(left,right,difference);
+       }
+    }
+    console.log(difference);
+    if(difference.length>0){
+        return Math.max(...difference);
+    }
+    else{
+        return 0;
+    }
+};
+console.log(maxProfit(prices));
\ No newline at end of file
diff --git a/challenge-3/index.js b/challenge-3/index.js
new file mode 100644
index 0000000..203d3b1
--- /dev/null
+++ b/challenge-3/index.js
@@ -0,0 +1,16 @@
+var containsDuplicate = function(nums) {
+    if(!Array.isArray(nums)){
+        return false;
+    }
+    let duplicate = new Map();
+    for(let num of nums){
+        duplicate.set(num,(duplicate.get(num)||0)+1);
+    }
+    for(let [key,value] of duplicate){
+        if(value>1){
+            return true;
+        }
+    }
+    return false;
+};
+console.log(containsDuplicate(nums));
\ No newline at end of file
diff --git a/challenge-4/index.js b/challenge-4/index.js
new file mode 100644
index 0000000..f3fceab
--- /dev/null
+++ b/challenge-4/index.js
@@ -0,0 +1,23 @@
+var productExceptSelf = function (nums) {
+    if (!Array.isArray(nums)) {
+        return 0;
+    }
+    let prefix = [1];
+    let suffix = [1];
+    let forward = 1;
+    let reverse = 1;
+    let value = 1;
+    let answer = [];
+    for(let i=1;i<nums.length;i++){
+        forward *= nums[i-1];
+        reverse *= nums[nums.length-i];
+        prefix.push(forward);
+        suffix.unshift(reverse)
+    }
+    for(let i=0;i<nums.length;i++){
+        value = prefix[i]*suffix[i];
+        answer.push(value);
+    }
+    return answer;
+};
+console.log(productExceptSelf(nums))
\ No newline at end of file