20251006 baekjoon

code_study/Baekjoon/swift/13172.swift

@@ -0,0 +1,57 @@
+let Mod = 1000000007
+
+func power(base a: Int, exponent b: Int) -> Int {
+    if b == 0 {
+        return 1
+    }
+    
+    if b == 1 {
+        return a
+    }
+    
+    var half = power(base: a, exponent: b/2)
+    half = (half * half) % Mod
+    
+    if b%2 == 1 {
+        return (a * half) % Mod
+    }
+    else {
+        return half
+    }
+}
+
+func gcd(_ x: Int, _ y: Int) -> Int {
+    var a = max(x,y)
+    var b = min(x,y)
+    
+    while b != 0 {
+        let r = a%b
+        a = b
+        b = r
+    }
+    
+    return a
+}
+
+if let M = Int(readLine() ?? "") {
+    var result = 0
+    
+    for _ in 0..<M {
+        if let input = readLine(),
+           let info = input.split(separator: " ").compactMap({Int($0)}) as? [Int],
+           info.count == 2
+        {
+            var N = info[0]
+            var S = info[1]
+            
+            let GCD = gcd(N, S)
+            N /= GCD
+            S /= GCD
+            
+            result += S*(power(base: N, exponent: Mod-2))%Mod
+            result %= Mod
+        }
+    }
+    
+    print(result)
+}