Create 2426-number-of-pairs-satisfying-inequality.js

Author: everthis

2426-number-of-pairs-satisfying-inequality.js

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+/**
+ * @param {number[]} nums1
+ * @param {number[]} nums2
+ * @param {number} diff
+ * @return {number}
+ */
+const numberOfPairs = function (nums1, nums2, diff) {
+  const n = nums1.length, limit = 6 * 1e4, add = 3 * 1e4
+  const bit = new BIT(limit)
+
+  let res = 0
+  for(let j = 0; j < n; j++) {
+    const d = nums1[j] - nums2[j] + add
+    res += bit.query(d + diff)
+    bit.update(d, 1)
+  }
+
+  return res
+}
+
+function lowBit(x) {
+  return x & -x
+}
+class BIT {
+  constructor(n) {
+    this.arr = Array(n + 1).fill(0)
+  }
+
+  update(i, delta) {
+    if(i < 1) return
+    while (i < this.arr.length) {
+      this.arr[i] += delta
+      i += lowBit(i)
+    }
+  }
+
+  query(i) {
+    let res = 0
+    if(i < 1) return res
+    while (i > 0) {
+      res += this.arr[i]
+      i -= lowBit(i)
+    }
+    return res
+  }
+}