Add solution #1712

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,494 LeetCode solutions in JavaScript
+# 1,495 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1319,6 +1319,7 @@
 1707|[Maximum XOR With an Element From Array](./solutions/1707-maximum-xor-with-an-element-from-array.js)|Hard|
 1710|[Maximum Units on a Truck](./solutions/1710-maximum-units-on-a-truck.js)|Easy|
 1711|[Count Good Meals](./solutions/1711-count-good-meals.js)|Medium|
+1712|[Ways to Split Array Into Three Subarrays](./solutions/1712-ways-to-split-array-into-three-subarrays.js)|Medium|
 1716|[Calculate Money in Leetcode Bank](./solutions/1716-calculate-money-in-leetcode-bank.js)|Easy|
 1718|[Construct the Lexicographically Largest Valid Sequence](./solutions/1718-construct-the-lexicographically-largest-valid-sequence.js)|Medium|
 1726|[Tuple with Same Product](./solutions/1726-tuple-with-same-product.js)|Medium|

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

@@ -0,0 +1,76 @@
+/**
+ * 1712. Ways to Split Array Into Three Subarrays
+ * https://leetcode.com/problems/ways-to-split-array-into-three-subarrays/
+ * Difficulty: Medium
+ *
+ * A split of an integer array is good if:
+ * - The array is split into three non-empty contiguous subarrays - named left, mid, right
+ *   respectively from left to right.
+ * - The sum of the elements in left is less than or equal to the sum of the elements in mid,
+ *   and the sum of the elements in mid is less than or equal to the sum of the elements in right.
+ *
+ * Given nums, an array of non-negative integers, return the number of good ways to split nums.
+ * As the number may be too large, return it modulo 109 + 7.
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var waysToSplit = function(nums) {
+  const MOD = 1e9 + 7;
+  const n = nums.length;
+  const prefixSum = new Array(n).fill(0);
+
+  prefixSum[0] = nums[0];
+  for (let i = 1; i < n; i++) {
+    prefixSum[i] = prefixSum[i - 1] + nums[i];
+  }
+
+  let splitCount = 0;
+  for (let i = 0; i < n - 2; i++) {
+    let left = i + 1;
+    let right = n - 2;
+    let validStart = -1;
+    let validEnd = -1;
+
+    while (left <= right) {
+      const mid = Math.floor((left + right) / 2);
+      const leftSum = prefixSum[i];
+      const midSum = prefixSum[mid] - prefixSum[i];
+      const rightSum = prefixSum[n - 1] - prefixSum[mid];
+
+      if (leftSum <= midSum && midSum <= rightSum) {
+        validStart = mid;
+        right = mid - 1;
+      } else if (leftSum > midSum) {
+        left = mid + 1;
+      } else {
+        right = mid - 1;
+      }
+    }
+
+    left = validStart === -1 ? n - 1 : validStart;
+    right = n - 2;
+
+    while (left <= right) {
+      const mid = Math.floor((left + right) / 2);
+      const leftSum = prefixSum[i];
+      const midSum = prefixSum[mid] - prefixSum[i];
+      const rightSum = prefixSum[n - 1] - prefixSum[mid];
+
+      if (leftSum <= midSum && midSum <= rightSum) {
+        validEnd = mid;
+        left = mid + 1;
+      } else {
+        right = mid - 1;
+      }
+    }
+
+    if (validStart !== -1 && validEnd !== -1 && validStart <= validEnd) {
+      splitCount = (splitCount + validEnd - validStart + 1) % MOD;
+    }
+  }
+
+  return splitCount;
+};