Create 3748-count-stable-subarrays.js

Author: everthis

3748-count-stable-subarrays.js

@@ -0,0 +1,70 @@
+/**
+ * @param {number[]} nums
+ * @param {number[][]} queries
+ * @return {number[]}
+ */
+var countStableSubarrays = function(nums, queries) {
+ let n = nums.length
+ const {floor: flr} = Math
+ let res = []
+ let segments = [], start = 0
+
+ for(let i = 0; i < n; i++) {
+ if(nums[i] < nums[i - 1]) {
+ segments.push([start, i - 1])
+ start = i
+ }
+ }
+ segments.push([start, n - 1])
+
+ let pc = []
+
+ let total = 0
+ for(const [s, e] of segments) {
+ let length = e - s + 1
+ let count = length * (length + 1) / 2
+ total += count
+ pc.push(total)
+ }
+
+ for(const [l, r] of queries) {
+ let li = bisect(segments, l) - 1
+ let ri = bisect(segments, r) - 1
+ if(li < 0) li = 0
+ if(ri < 0) ri = 0
+ if(li === ri) {
+ let [ss, se] = segments[li]
+ let length = r - l + 1
+ let count = length * (length + 1) / 2
+ res.push(count)
+ } else {
+ let [ss, se] = segments[li]
+ let ll = se - l + 1
+ let lc = ll * (ll + 1) / 2
+
+ let [ssr, ser] = segments[ri]
+ let rl = r - ssr + 1
+ let rc = rl * (rl + 1) / 2
+
+ let mid_count = 0
+ if(ri - li > 1) {
+ mid_count = pc[ri - 1] - pc[li]
+ }
+ res.push(lc + mid_count + rc)
+ }
+
+ }
+ 
+ return res
+
+ function bisect(segments, x) {
+ let low = 0, high = segments.length
+ while(low < high) {
+ let mid = flr((low + high) / 2)
+ if(segments[mid][0] <= x) low = mid + 1
+ else high = mid
+ }
+
+ return low
+ }
+};