Update 1012-numbers-with-repeated-digits.js

Author: everthis

1012-numbers-with-repeated-digits.js

@@ -1,3 +1,67 @@
+/**
+ * @param {number} n
+ * @return {number}
+ */
+function numDupDigitsAtMostN(n) {
+  let numNoDupDigits = 0; // the number of positive integers less than or equal to n with no repeated digits
+
+  let lst = Array.from(String(n), Number);
+  let n_digits = lst.length;
+
+  // if n = 8765, lst = [8,7,6,5],
+  // the number without repeated digit can the the following format:
+  // XXX
+  // XX
+  // X
+  for (let i = 1; i < n_digits; i++) {
+    // the number of i digits without repeated digit
+    // the leading digit cannot be 0
+    numNoDupDigits += 9 * perm(9, i - 1);
+  }
+
+  // and
+  // 1XXX ~ 7XXX
+  // 80XX ~ 86XX
+  // 870X ~ 875X
+  // 8760 ~ 8764
+  let seen = new Set();
+  for (let i = 0; i < lst.length; i++) {
+    let x = lst[i];
+    for (let y = (i === 0 ? 1 : 0); y < x; y++) {
+      if (!seen.has(y)) {
+        // the leading digit used - y
+        // for the remaining positions we cannot use digits in set seen and y
+        numNoDupDigits += perm(9 - i, n_digits - i - 1);
+      }
+    }
+    if (seen.has(x)) {
+      break;
+    }
+    seen.add(x);
+  }
+
+  // and
+  // 8765
+  if (n_digits === new Set(lst).size) {
+    numNoDupDigits += 1;
+  }
+
+  return n - numNoDupDigits;
+}
+
+function perm(m, n) {
+  let res = 1
+  for(let i = 0; i < n; i++) {
+    res *= m
+    m--
+  }
+
+  return res
+}
+
+// another
+
+
 /**
  * @param {number} n
  * @return {number}