pb4

Author: EISAWESOME

README.md

@@ -47,5 +47,20 @@ The following test should pass:
 node = Node('root', Node('left', Node('left.left')), Node('right'))
 assert deserialize(serialize(node)).left.left.val == 'left.left'
 ```
+
 ### Solution
+
 [JS](pb3/answer.js) (5:12)
+
+
+## 4
+>This problem was asked by Stripe.
+
+Given an array of integers, find the first missing positive integer in linear time and constant space. In other words, find the lowest positive integer that does not exist in the array. The array can contain duplicates and negative numbers as well.
+For example, the input `[3, 4, -1, 1]` should give `2`. The input `[1, 2, 0]` should give `3`.
+You can modify the input array in-place.
+
+### Solution
+
+[JS](pb4/answer.js) (3:47)
+

pb4/Problem.md

@@ -0,0 +1,5 @@
+>This problem was asked by Stripe.
+
+Given an array of integers, find the first missing positive integer in linear time and constant space. In other words, find the lowest positive integer that does not exist in the array. The array can contain duplicates and negative numbers as well.
+For example, the input `[3, 4, -1, 1]` should give `2`. The input `[1, 2, 0]` should give `3`.
+You can modify the input array in-place.

pb4/answer.js

@@ -0,0 +1,20 @@
+
+// Time : 3:47
+const input1 = [3, 4, -1, 1];
+const input2 = [1, 2, 0];
+
+const pb4 = (input) => {
+  // Filter out negative elements
+  const onlyPositives = input.filter( el => el > 0 );
+  let i = 1;
+  // Give the loop some limit
+  while(i < 1000000000){
+    if(!onlyPositives.includes(i))
+      //Starts at 1, returns whenever an integer is missing
+      return i;
+    i++;
+  }  
+}
+
+console.log(pb4(input1));
+console.log(pb4(input2));