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

Author: everthis

1012-numbers-with-repeated-digits.js

@@ -0,0 +1,32 @@
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var numDupDigitsAtMostN = function(n) {
+  const digits = [], {floor} = Math
+  let tmp = n + 1
+  while(tmp) {
+    digits.push(tmp % 10)
+    tmp = floor(tmp / 10)
+  }
+  let res = 0
+  const len = digits.length
+  let cur = 9
+  for(let i = 0; i < len - 1; i++) {
+    res += cur
+    cur *= (9 - i)
+  }
+  cur = floor(cur / 9)
+  const seen = Array(10).fill(false)
+  for(let i = 0; i < len; i++) {
+    const d = digits[len - i - 1]
+    for(let j = (i === 0 ? 1 : 0); j < d; j++) {
+      if(!seen[j]) res += cur
+    }
+    cur = floor(cur / (9 - i))
+    if(seen[d]) break
+    seen[d] = true
+  }
+
+  return n - res
+};