Complete No.19 and No.21 questions.

README.md

@@ -0,0 +1 @@
+# Algorithm Exercise of the book: *Coding Interviews: Questions, Analysis and Solutions*

src/chapter-3/19_match_regular_expression.cpp

@@ -7,10 +7,43 @@
  * 例如，字符串"aaa"与模式"a.a"和"ab*ac*a"匹配，但与"aa.a"和"ab*a"均不匹配。
  */
 
-bool solution::MatchRegularExpression(string str, string pattern) {
-    if(str== ""||pattern==""){
+// NOT PASS
+bool solution::MatchRegularExpression(string s, string p) {
+    if (s.empty() && p.empty()) {
+        return true;
+    }
+
+    if (!s.empty() && p.empty()) {
         return false;
     }
 
+    if (p[1] == '*') {
+        if (p[0] == s[0] || (p[0] == '.' && !s.empty())) {
+            // 完成匹配，进入下一状态
+            bool res1 = MatchRegularExpression(CutString(s, 1), CutString(p, 2));
+            // 保持当前状态
+            bool res2 = MatchRegularExpression(CutString(s, 1), p);
+            // 忽略*，进入下一状态
+            bool res3 = MatchRegularExpression(s, CutString(p, 2));
+
+            return res1 || res2 || res3;
+        } else {
+            // 忽略*，进入下一状态
+            bool res = MatchRegularExpression(s, CutString(p, 2));
+            return res;
+        }
+    }
+
+    if (p[0] == s[0] || (p[0] == '.' && !s.empty())) {
+        // 完成匹配，进入下一状态
+        bool res = MatchRegularExpression(CutString(s, 1), CutString(p, 1));
+        return res;
+    }
+
+    return false;
+}
 
+string solution::CutString(string& s, int n) {
+    string newStr;
+    return newStr.assign(s, n, s.length() - n);
 }

src/chapter-3/21_reorder_odd_even.cpp

@@ -0,0 +1,36 @@
+#include "solution.h"
+
+/*
+ * 21. 调整数组顺序使奇数位于偶数前面
+ * 输入一个整数数组，实现一个函数来调整该数组中数字的顺序，使得所有奇数在数组的前半部分，所有偶数在数组的后半部分。
+ */
+
+vector<int> solution::Reorder(vector<int>& nums) {
+    if (nums.empty()) {
+        return nums;
+    }
+
+    auto pBegin = nums.begin();
+    auto pEnd = --nums.end();
+    auto IsOdd = [](int num) -> bool {
+        return num % 2 == 1;
+    };
+
+    while (pBegin < pEnd) {
+        while (pBegin < pEnd && IsOdd(*pBegin)) {
+            pBegin++;
+        }
+
+        while (pBegin < pEnd && !IsOdd(*pEnd)) {
+            pEnd--;
+        }
+
+        if (pBegin < pEnd) {
+            int temp = *pBegin;
+            *pBegin = *pEnd;
+            *pEnd = temp;
+        }
+    }
+
+    return nums;
+}

src/include/solution.h

@@ -90,7 +90,9 @@ ListNode* DeleteNode(ListNode* head, int val);
 void DeleteDuplication(ListNode** pHead);
 
 // Question 19
-bool MatchRegularExpression(string str, string pattern);
+bool MatchRegularExpression(string s, string p);
+
+string CutString(string& s, int n);
 
 // Question 20
 bool IsNumber(string s);
@@ -100,4 +102,7 @@ string CutNumString(string& s);
 bool ScanInteger(string& s);
 
 bool ScanUnsignedInteger(string& s);
+
+// Question 21
+vector<int> Reorder(vector<int>& nums);
 }

src/main.cpp

@@ -7,6 +7,10 @@ using namespace solution;
 using namespace ds;
 
 int main() {
+    std::string str = "";
+    std::string pattern = "";
+    bool res = solution::MatchRegularExpression(str, pattern);
+    std::cout << res << std::endl;
 
     return 0;
 }