Create 1712-ways-to-split-array-into-three-subarrays.js

Author: everthis

1712-ways-to-split-array-into-three-subarrays.js

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+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+const waysToSplit = function (nums) {
+  const N = nums.length
+  let ret = 0
+  const presum = Array(N + 1).fill(0)
+  for (let i = 0; i < N; i++) presum[i + 1] = presum[i] + nums[i]
+  let avg = (presum[N] / 3 + 1) >> 0
+  for (let l = 1, r = 2, rr = 2; l < N - 1; l++) {
+    if (presum[l] > avg) break
+    while (r < N && presum[l] > presum[r] - presum[l]) r++
+    r = Math.max(r, l + 1)
+    if (r > rr) rr = r
+    while (rr < N && presum[N] - presum[rr] >= presum[rr] - presum[l]) rr++
+    ret += rr - r
+    if (ret >= 1000000007) ret -= 1000000007
+  }
+  return ret
+}