Create 2090-k-radius-subarray-averages.js

Author: everthis

2090-k-radius-subarray-averages.js

@@ -0,0 +1,43 @@
+const lowBit = (x) => x & -x
+class FenwickTree {
+  constructor(n) {
+    if (n < 1) return
+    this.sum = Array(n + 1).fill(0)
+  }
+  update(i, delta) {
+    if (i < 1) return
+    while (i < this.sum.length) {
+      this.sum[i] += delta
+      i += lowBit(i)
+    }
+  }
+  query(i) {
+    if (i < 1) return 0
+    let sum = 0
+    while (i > 0) {
+      sum += this.sum[i]
+      i -= lowBit(i)
+    }
+    return sum
+  }
+}
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+const getAverages = function(nums, k) {
+  const n = nums.length
+  const bit = new FenwickTree(n)
+  for(let i = 0; i < n; i++) {
+    bit.update(i + 1, nums[i])
+  }
+  const res = Array(n).fill(-1)
+  // console.log(bit)
+  for(let i = k; i < n - k; i++) {
+    const pre = bit.query(i + 1 - k - 1), cur = bit.query(i + 1 + k)
+    res[i] = ~~((cur - pre) / (k * 2 + 1))
+  }
+  
+  return res
+};