Update 1425-constrained-subsequence-sum.js

Author: everthis

1425-constrained-subsequence-sum.js

@@ -20,3 +20,80 @@ const constrainedSubsetSum = function(nums, k) {
     }
     return max;
 };
+
+// another
+
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+const constrainedSubsetSum = function (nums, k) {
+  const dll = new DLL()
+  dll.push([0, nums[0]])
+  let max = nums[0]
+  for (let i = 1; i < nums.length; i++) {
+    // console.log(dll, dll.peek())
+    let [index, lastKsum] = dll.peek().val
+
+    if (index == i - k) {
+      dll.shift()
+    }
+    const sum = Math.max(lastKsum, 0) + nums[i]
+    max = Math.max(max, sum)
+    while (!dll.isEmpty() && dll.peekLast().val[1] < sum) {
+      dll.pop()
+    }
+    dll.push([i, sum])
+  }
+  return max
+}
+
+class Node {
+  constructor(val) {
+    this.val = val
+    this.prev = null
+    this.next = null
+  }
+}
+class DLL {
+  constructor() {
+    this.head = new Node()
+    this.tail = null
+  }
+  peek() {
+    return this.head.next
+  }
+  peekLast() {
+    return this.tail
+  }
+  isEmpty() {
+    return this.head.next == null
+  }
+  shift() {
+    const h = this.head.next
+    if (h) {
+      this.head.next = h.next
+      if (h.next) {
+        h.next.prev = this.head
+      } else {
+        this.tail = null
+      }
+    }
+  }
+  pop() {
+    if (this.tail == null) return
+    const newTail = this.tail.prev
+    if (newTail) {
+      newTail.next = null
+      this.tail.prev = null
+      this.tail = newTail
+    }
+  }
+  push(val) {
+    const node = new Node(val)
+    node.prev = this.tail ?? this.head
+    node.prev.next = node
+    this.tail = node
+  }
+}