added add_digit_anywhere_primes to c++

cpp/add_digit_anywhere_primes/Makefile

@@ -0,0 +1,23 @@
+# rename `template` to name of project
+TARGET=add_digit_anywhere_primes
+CXX=g++
+OFILES=../common/tree.o ../common/util.o
+LIBS=
+CXXFLAGS=-g
+
+$(TARGET): $(OFILES) $(TARGET).o
+	$(CXX) $(CXXFLAGS) -o $@ $(TARGET).o $(OFILES) $(LIBS)
+
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c -o $@ $<
+
+PHONY: clean run all
+
+clean:
+	rm *.o $(TARGET)
+
+run:
+	./$(TARGET)
+
+all:
+	make $(TARGET)

cpp/add_digit_anywhere_primes/add_digit_anywhere_primes.cpp

@@ -0,0 +1,35 @@
+/* include little library I made */
+#include "../common/util.h"
+#include "../common/tree.h"
+#include <string>
+
+auto next(ull x) -> std::vector<ull> {
+    std::vector<ull> new_xs;
+    ull temp;
+    std::string str_x = std::to_string(x);
+    for (int i = 0; i < str_x.length(); i++) {
+        for (int d = 0; d < 10; d++) {
+            if (!(i == 0 && d == 0)) {
+                str_x = std::to_string(x);
+                str_x.insert(i, std::to_string(d));
+                /* std::cout << x << ' ' << str_x << ' ' << i << ' ' << d << '\n'; */
+                temp = std::stoull(str_x);
+                if (is_prime(temp)) {
+                    new_xs.push_back(temp);
+                }
+            }
+        }
+    }
+    return new_xs;
+}
+
+auto main() -> int {
+    /* starts off with a tree with value 0 and no children and searches 20
+     * iterations, feel free to tweak to whatever you want
+     */
+    Tree tree(0, {2, 3, 5, 7});
+    for (int i = 0; i < 20; i++) {
+        tree.step(next);
+        print_vec(tree.longest_path());
+    }
+}