440:字典序的第K小数字

src/main/java/leetcode/editor/cn/KThSmallestInLexicographicalOrder.java

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+//给定整数 n 和 k，返回 [1, n] 中字典序第 k 小的数字。 
+//
+// 
+//
+// 示例 1: 
+//
+// 
+//输入: n = 13, k = 2
+//输出: 10
+//解释: 字典序的排列是 [1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9]，所以第二小的数字是 10。
+// 
+//
+// 示例 2: 
+//
+// 
+//输入: n = 1, k = 1
+//输出: 1
+// 
+//
+// 
+//
+// 提示: 
+//
+// 
+// 1 <= k <= n <= 10⁹ 
+// 
+// Related Topics 字典树 👍 389 👎 0
+
+package leetcode.editor.cn;
+
+//440:字典序的第K小数字
+public class KThSmallestInLexicographicalOrder {
+    public static void main(String[] args) {
+        Solution solution = new KThSmallestInLexicographicalOrder().new Solution();
+        // TO TEST
+        System.out.println(solution.findKthNumber(13, 2));
+        System.out.println(solution.findKthNumber(1, 1));
+        System.out.println(solution.findKthNumber(100, 90));
+        System.out.println(solution.findKthNumber(10000, 10000));
+    }
+
+    //leetcode submit region begin(Prohibit modification and deletion)
+    class Solution {
+        public int findKthNumber(int n, int k) {
+            for (int i = 1; i <= n; i++) {
+                if (k == 1) {
+                    return i;
+                }
+                int count = getCount(i, n);
+                if (count < k) {
+                    k -= count;
+                } else {
+                    i = i * 10 - 1;
+                    k--;
+                }
+            }
+            return 0;
+        }
+
+        public int getCount(int num, long n) {
+            int count = 0;
+            long min = num;
+            long max = num;
+            while (min <= n) {
+                count += Math.min(max, n) - min + 1;
+                min = min * 10;
+                max = max * 10 + 9;
+            }
+            return count;
+        }
+
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}

src/main/java/leetcode/editor/cn/doc/content/KThSmallestInLexicographicalOrder.md

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+<p>给定整数&nbsp;<code>n</code>&nbsp;和&nbsp;<code>k</code>，返回&nbsp;&nbsp;<code>[1, n]</code>&nbsp;中字典序第&nbsp;<code>k</code>&nbsp;小的数字。</p>
+
+<p>&nbsp;</p>
+
+<p><strong>示例 1:</strong></p>
+
+<pre>
+<strong>输入: </strong>n = 13, k = 2
+<strong>输出: </strong>10
+<strong>解释: </strong>字典序的排列是 [1, 10, 11, 12, 13, 2, 3, 4, 5, 6, 7, 8, 9]，所以第二小的数字是 10。
+</pre>
+
+<p><strong>示例 2:</strong></p>
+
+<pre>
+<strong>输入:</strong> n = 1, k = 1
+<strong>输出:</strong> 1
+</pre>
+
+<p>&nbsp;</p>
+
+<p><strong>提示:</strong></p>
+
+<ul>
+	<li><code>1 &lt;= k &lt;= n &lt;= 10<sup>9</sup></code></li>
+</ul>
+<div><div>Related Topics</div><div><li>字典树</li></div></div><br><div><li>👍 389</li><li>👎 0</li></div>