cpp: add «402. Remove K Digits»

Signed-off-by: Matej Focko <mfocko@redhat.com>

cpp/remove-k-digits.cpp

@@ -0,0 +1,56 @@
+#include <algorithm>
+#include <string>
+#include <vector>
+
+class Solution {
+    static bool nonZero(char c) { return c != '0'; }
+
+  public:
+    std::string removeKdigits(const std::string &num, int k) {
+        if (static_cast<int>(num.size()) <= k) {
+            return "0";
+        }
+
+        std::vector<char> digits;
+        for (auto d : num) {
+            while (k > 0 && !digits.empty() && d < digits.back()) {
+                --k;
+                digits.pop_back();
+            }
+            digits.push_back(d);
+        }
+
+        while (k-- > 0) {
+            digits.pop_back();
+        }
+
+        if (auto it = std::find_if(digits.begin(), digits.end(), nonZero);
+            it != digits.end()) {
+            return std::string(it, digits.end());
+        }
+
+        return "0";
+    }
+};
+
+#ifdef _MF_TEST
+#include <gtest/gtest.h>
+
+TEST(examples, no_1) {
+    Solution s;
+    EXPECT_EQ(s.removeKdigits("1432219", 3), "1219");
+}
+TEST(examples, no_2) {
+    Solution s;
+    EXPECT_EQ(s.removeKdigits("10200", 1), "200");
+}
+TEST(examples, no_3) {
+    Solution s;
+    EXPECT_EQ(s.removeKdigits("10", 2), "0");
+}
+
+int main(int argc, char **argv) {
+    testing::InitGoogleTest(&argc, argv);
+    return RUN_ALL_TESTS();
+}
+#endif