LC 525: Contiguous Array

findMaxLength.js

@@ -0,0 +1,32 @@
+/**
+ * @param {number[]} nums
+ * @return {number}
+Intution: 
+I use a prefix sum approach with a hash map to track the difference between the number of 1s and 0s seen so far.
+I treat each 1 as +1 and each 0 as -1.
+To handle subarrays that start at index 0, I initialize the running count to 1 and store this count at index -1 in the hash map. 
+
+As I iterate through the array, I update the running count based on the current value.
+If the same count has been seen before, it means the subarray between the previous index and the current index has an equal number of 0s and 1s. I compute the length of this subarray and update the maximum length.
+
+I only store the first occurrence of each count in the hash map to make sure the longest possible subarray is captured.
+
+Finally, I return the maximum length found.
+ */
+
+var findMaxLength = function (nums) {
+    let hashMap = new Map();
+    hashMap.set(1, -1);
+    let currCount = 1;
+    let maxLength = 0;
+    for (let idx = 0; idx < nums.length; idx++) {
+        currCount += nums[idx] === 0 ? -1 : 1;
+        if (hashMap.has(currCount)) {
+            maxLength = Math.max(maxLength, idx - hashMap.get(currCount));
+        } else {
+            hashMap.set(currCount, idx);
+        }
+    }
+
+    return maxLength;
+};