2961. Double Modular Exponentiation

Author: sergeyleschev

2501-3000/2961. Double Modular Exponentiation.swift

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+class Solution {
+
+    // Solution by Sergey Leschev
+    // 2961. Double Modular Exponentiation
+
+    func getGoodIndices(_ variables: [[Int]], _ target: Int) -> [Int] {
+        var result: [Int] = []
+
+        func power(_ b: Int, _ p: Int, _ m: Int) -> Int {
+            if p <= 0 {
+                return 1
+            }
+            var t = power(b, p / 2, m)
+            t = ((t * t) % m)
+            return (p % 2 == 1) ? (t * b) % m : t
+        }
+
+        for i in 0..<variables.count {
+            let a = variables[i][0] % 10
+            let b = variables[i][1]
+            let c = variables[i][2]
+            let m = variables[i][3]
+
+            var t = power(a, b, 10)
+            t = power(t, c, m)
+
+            if t == target {
+                result.append(i)
+            }
+        }
+
+        return result
+    }
+}