permutation.js

amit265 · amit265 · commit 058e0e34e964 · 2026-01-27T01:50:41.000+05:30
diff --git a/javascript/3_math-programs/permutation.js b/javascript/3_math-programs/permutation.js
@@ -0,0 +1,30 @@
+// 20. Calculate nPr (Permutations)
+
+//P(n, r) = n! / (n - r)!   for n >= r >= 0
+
+function permutation(n, r) {
+  if (n < r) return -1;
+  return factorial(n) / factorial(n - r);
+}
+
+function factorial(n) {
+  return n <= 1 ? 1 : n * factorial(n - 1);
+}
+
+console.log(permutation(13, 2));
+
+// using for loop
+
+function permutations(n, r) {
+    if(n < r) return -1;
+
+    let result = n;
+
+    for(let i = 1; i < r; i++){
+        result *= n - i;
+    }
+    return result;
+}
+
+
+console.log("4 P 1: ", permutation(4, 1))
