2963. Count the Number of Good Partitions

Author: sergeyleschev

2501-3000/2963. Count the Number of Good Partitions.swift

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+class Solution {
+
+    // Solution by Sergey Leschev
+    // 2963. Count the Number of Good Partitions
+
+    // Time complexity - O(N)
+    // Space complexity - O(N)
+
+    func numberOfGoodPartitions(_ nums: [Int]) -> Int {
+        let m = 1_000_000_007
+        var count = 0
+        var last: [Int: Int] = [:]
+
+        for i in 0..<nums.count {
+            last[nums[i]] = i
+        }
+
+        var next = -1
+
+        for i in 0..<nums.count {
+            if i > next {
+                count += 1
+            }
+            next = max(next, last[nums[i]]!)
+        }
+
+        return power(2, count - 1, m)
+    }
+
+    func power(_ b: Int, _ p: Int, _ m: Int) -> Int {
+        if p <= 0 {
+            return 1
+        }
+        let t = power(b, p / 2, m)
+        return (p % 2 == 1) ? (((t * t) % m) * b) % m : (t * t) % m
+    }
+}