Create 440-k-th-smallest-in-lexicographical-order.js

Author: everthis

440-k-th-smallest-in-lexicographical-order.js

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+/**
+ * @param {number} n
+ * @param {number} k
+ * @return {number}
+ */
+const findKthNumber = function(n, k) {
+  let curr = 1
+  k = k - 1
+  while (k > 0) {
+    let steps = calSteps(n, curr, curr + 1)
+    if (steps <= k) {
+      curr++
+      k -= steps
+    } else {
+      curr *= 10
+      k--
+    }
+  }
+  return curr
+}
+
+//use long in case of overflow
+function calSteps(n, n1, n2) {
+  let steps = 0
+  while (n1 <= n) {
+    steps += Math.min(n + 1, n2) - n1
+    n1 *= 10
+    n2 *= 10
+  }
+  return steps
+}