Add C++ solution for leetcofde 1003.

Author: yanglr

cpp-leetcode/leetcode1003-check-if-word-is-valid-after-substitutions_stack.cpp

@@ -0,0 +1,31 @@
+#include<vector>
+#include<algorithm>
+#include<iostream>
+using namespace std;
+
+class Solution {
+public:
+    bool isValid(string s) {
+        string stk; // 用string模拟栈
+        for (auto& c: s) {
+            stk += c;
+            if (stk.size() >= 3 && stk.substr(stk.size() - 3) == "abc")
+            {
+                for (int i = 0; i < 3; i++)
+                    stk.pop_back();
+            }
+        }
+        return stk.empty();
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    string s = "abcabcababcc";
+    auto res = sol.isValid(s);
+    cout << (res ? "True" : "False") << endl;
+    
+    return 0;
+}