feat: add cpp solution to lcof problems: No.44,46

Author: maolonglong

lcof/面试题44. 数字序列中某一位的数字/README.md

@@ -119,6 +119,27 @@ var findNthDigit = function (n) {
 };
 ```
 
+### **C++**
+
+```cpp
+class Solution {
+public:
+    int findNthDigit(int n) {
+        int digit = 1;
+        long long start = 0;
+        long long count = 10;
+        while (n > count) {
+            n -= count;
+            ++digit;
+            start = start == 0 ? 10 : start * 10;
+            count = 9 * start * digit;
+        }
+        long long num = start + n / digit;
+        return to_string(num)[n % digit] - '0';
+    }
+};
+```
+
 ### **...**
 
 ```

lcof/面试题44. 数字序列中某一位的数字/Solution.cpp

@@ -0,0 +1,16 @@
+class Solution {
+public:
+    int findNthDigit(int n) {
+        int digit = 1;
+        long long start = 0;
+        long long count = 10;
+        while (n > count) {
+            n -= count;
+            ++digit;
+            start = start == 0 ? 10 : start * 10;
+            count = 9 * start * digit;
+        }
+        long long num = start + n / digit;
+        return to_string(num)[n % digit] - '0';
+    }
+};

lcof/面试题46. 把数字翻译成字符串/README.md

@@ -88,6 +88,41 @@ var translateNum = function (num) {
 };
 ```
 
+### **C++**
+
+注释的代码是一维 dp ，因为 `dp[i]` 只依赖 `dp[i - 1]` 和 `dp[i - 2]` ，所以可以进一步压缩空间。
+
+```cpp
+class Solution {
+public:
+    int translateNum(int num) {
+        // string s = to_string(num);
+        // int n = s.size();
+        // vector<int> dp(n + 1);
+        // dp[0] = dp[1] = 1;
+        // for (int i = 2; i <= n; ++i) {
+        //     dp[i] = dp[i - 1];
+        //     if (s[i - 2] == '1' || s[i - 2] == '2' && s[i - 1] < '6') {
+        //         dp[i] += dp[i - 2];
+        //     }
+        // }
+        // return dp[n];
+        string s = to_string(num);
+        int n = s.size();
+        int dp_0 = 1, dp_1 = 1, dp_2 = 1;
+        for (int i = 2; i <= n; ++i) {
+            dp_2 = dp_1;
+            if (s[i - 2] == '1' || s[i - 2] == '2' && s[i - 1] < '6') {
+                dp_2 += dp_0;
+            }
+            dp_0 = dp_1;
+            dp_1 = dp_2;
+        }
+        return dp_2;
+    }
+};
+```
+
 ### **...**
 
 ```

lcof/面试题46. 把数字翻译成字符串/Solution.cpp

@@ -0,0 +1,28 @@
+class Solution {
+public:
+    int translateNum(int num) {
+        // string s = to_string(num);
+        // int n = s.size();
+        // vector<int> dp(n + 1);
+        // dp[0] = dp[1] = 1;
+        // for (int i = 2; i <= n; ++i) {
+        //     dp[i] = dp[i - 1];
+        //     if (s[i - 2] == '1' || s[i - 2] == '2' && s[i - 1] < '6') {
+        //         dp[i] += dp[i - 2];
+        //     }
+        // }
+        // return dp[n];
+        string s = to_string(num);
+        int n = s.size();
+        int dp_0 = 1, dp_1 = 1, dp_2 = 1;
+        for (int i = 2; i <= n; ++i) {
+            dp_2 = dp_1;
+            if (s[i - 2] == '1' || s[i - 2] == '2' && s[i - 1] < '6') {
+                dp_2 += dp_0;
+            }
+            dp_0 = dp_1;
+            dp_1 = dp_2;
+        }
+        return dp_2;
+    }
+};