Create 1015-numbers-with-repeated-digits.js

Author: everthis

1015-numbers-with-repeated-digits.js

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+/**
+ * @param {number} N
+ * @return {number}
+ */
+const numDupDigitsAtMostN = function(N) {
+  const L = [];
+  for (let x = N + 1; x > 0; x = Math.floor(x / 10)) L.unshift(x % 10);
+
+  // Count the number with digits < N
+  let res = 0,
+    n = L.length;
+  for (let i = 1; i < n; ++i) res += 9 * A(9, i - 1);
+
+  const seen = new Set();
+  for (let i = 0; i < n; ++i) {
+    for (let j = i > 0 ? 0 : 1; j < L[i]; ++j)
+      if (!seen.has(j)) res += A(9 - i, n - i - 1);
+    if (seen.has(L[i])) break;
+    seen.add(L[i]);
+  }
+  return N - res;
+};
+
+function A(m, n) {
+  return n === 0 ? 1 : A(m, n - 1) * (m - n + 1);
+}