开始计概A下半学期。

dsa/ch4_string/template_kmp_standard_next.cpp

@@ -0,0 +1,74 @@
+#include <iostream>
+#include <vector>
+
+std::vector<int> get_next_vector(const std::string& s) {
+    std::vector<int> next(s.size() + 1);
+    next[0] = -1;
+    for (int i = 0; i < next.size() - 1; i++) { // 实际上写入下一位
+        int j = next[i];
+        while (j != -1 && s[i] != s[j]) { // j = -1: 完全不匹配，s[i]==s[j]: 直接能用
+            j = next[j];
+        }
+        if (j == -1 || s[i] == s[j]) { j++; }
+        next[i + 1] = j;
+    }
+    return next;
+}
+
+std::vector<int> get_optimized_next_vector(const std::string& s, const std::vector<int>& next) {
+    std::vector<int> next_optimized(next.size());
+    next_optimized[0] = -1;
+    next_optimized[next.size() - 1] = next[next.size() - 1];
+    for (int i = 1; i < next.size() - 1; i++) {
+        if (s[next[i]] == s[i]) {
+            next_optimized[i] = next_optimized[next[i]];
+        } else {
+            next_optimized[i] = next[i];
+        }
+    }
+    return next_optimized;
+}
+
+std::vector<int> find_substring_pos(const std::string& target, const std::string& pattern) {
+    std::vector<int> matched_pos;
+    const std::vector<int> next_vector = get_optimized_next_vector(pattern, get_next_vector(pattern));
+    int j = 0;
+    for (int i = 0; i < target.size(); i++) {
+        while (j > -1 && target[i] != pattern[j]) {
+            j = next_vector[j];
+        }
+        if (j == -1) {
+            j = 0;  // 完全失配，直接 i++ j++
+            continue;
+        }
+        if (target[i] == pattern[j]) { j++; }
+        if (j == pattern.size()) {
+            matched_pos.push_back(i - static_cast<int>(pattern.size()) + 1);
+            j = next_vector[j];
+        }
+    }
+    return matched_pos;
+}
+
+std::ostream& operator<<(std::ostream& os, std::vector<int> vec) {
+    for (const auto& elem : vec) {
+        os << elem << " ";
+    }
+    return os;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::string target, pattern;
+    std::cin >> target >> pattern;
+    std::clog << get_next_vector(pattern) << std::endl;
+    std::clog << get_optimized_next_vector(pattern, get_next_vector(pattern)) << std::endl;
+    for (const auto i : find_substring_pos(target, pattern)) {
+        std::cout << i << " ";
+    }
+    std::cout << std::endl;
+
+    return 0;
+}