java: add «440. K-th Smallest in Lexicographical Order»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/k-th-smallest-in-lexicographical-order.java

@@ -0,0 +1,31 @@
+class Solution {
+  private int distance(int upperBound, long left, long right) {
+    var dist = 0;
+
+    for (; left <= upperBound; left *= 10, right *= 10) {
+      dist += Math.min(upperBound + 1, right) - left;
+    }
+
+    return dist;
+  }
+
+  public int findKthNumber(int n, int k) {
+    var current = 1;
+    --k;
+
+    while (k > 0) {
+      var d = distance(n, current, current + 1);
+
+      if (d <= k) {
+        // skipping d numbers at once
+        ++current;
+        k -= d;
+      } else {
+        current *= 10;
+        --k;
+      }
+    }
+
+    return current;
+  }
+}