Create 440. K-th Smallest in Lexicographical Order1 (#592)

Author: Chayandas07

440. K-th Smallest in Lexicographical Order1

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+class Solution {
+public:
+    long countSteps(long prefix, long n) {
+        long steps = 0, nextPrefix = prefix + 1;
+        while (prefix <= n) {
+            steps += min(n + 1, nextPrefix) - prefix;
+            prefix *= 10;
+            nextPrefix *= 10;
+        }
+        return steps;
+    }
+
+    int findKthNumber(int n, int k) {
+        int curr = 1;
+        k--;
+        while (k > 0) {
+            long steps = countSteps(curr, n);
+            if (steps <= k) {
+                curr++;
+                k -= steps;
+            } else {
+                curr *= 10;
+                k--;
+            }
+        }
+        return curr;
+    }
+};