Create csr.hpp

data_structure/csr.hpp

@@ -0,0 +1,50 @@
+#pragma once
+
+#include<vector>
+#include<ranges>
+#include<cassert>
+#include<utility>
+
+namespace noya2 {
+
+template<class E>
+struct csr {
+    csr (int n_ = 0, int m_ = -1) : n(n_), m(m_) {
+        if (m >= 0){
+            es.reserve(m);
+            start.reserve(m);
+        }
+        if (m == 0){
+            build();
+        }
+    }
+    int add(int idx, E elem){
+        int eid = start.size();
+        es.emplace_back(elem);
+        start.emplace_back(idx);
+        if (eid+1 == m) build();
+        return eid;
+    }
+    void build(){
+        if (m == -2) return ;
+        m = start.size();
+        std::vector<E> nes(m);
+        std::vector<int> nstart(n+2,0);
+        for (int i = 0; i < m; i++) nstart[start[i]+2]++;
+        for (int i = 1; i < n; i++) nstart[i+2] += nstart[i+1];
+        for (int i = 0; i < m; i++) nes[nstart[start[i]+1]++] = es[i];
+        swap(es,nes);
+        swap(start,nstart);
+        m = -2;
+    }
+    const auto operator[](int idx) const {
+        assert(m == -2);
+        return std::ranges::subrange(es.begin()+start[idx],es.begin()+start[idx+1]);
+    }
+  private:
+    int n, m;
+    std::vector<E> es;
+    std::vector<int> start;
+};
+
+} // namespace noya2