hashing example

hashing.cpp

@@ -0,0 +1,71 @@
+#include <cstdio>
+
+using namespace std;
+
+template<
+    typename TElem,
+    std::size_t NSize>
+class HashList {
+private:
+    typedef struct {
+        std::size_t index;
+        TElem elem;
+    } entry;
+
+    entry* entries[NSize];
+
+    std::size_t create_hash(std::size_t const index, std::size_t const e) {
+        return (index + e) % NSize;
+    }
+
+public:
+    HashList() {
+        for(std::size_t i = 0; i < NSize; i++) entries[i] = NULL;
+    }
+    bool insert(std::size_t index, TElem elem) {
+        std::size_t hash = 0;
+        std::size_t e = 0;
+
+        for(; e < NSize; e++) {
+            hash = this->create_hash(index, e);
+            if(entries[hash] == NULL) break;
+        }
+        
+        printf("Inserting %d had %d collisions\n", index, e);
+
+        if(entries[hash] != NULL) return false;
+
+        entries[hash] = new entry{index,elem};
+        return true;
+    }
+
+    entry* find(std::size_t index) {
+        std::size_t hash = 0;
+        std::size_t e = 0;
+        for(; e < NSize; e++) {
+            hash = this->create_hash(index, e);
+            if(entries[hash] == NULL || entries[hash]->index == index) break;
+        }
+        printf("Finding %d had %d collisions\n", index, e);
+
+        if(entries[hash] != NULL && entries[hash]->index != index) return NULL;
+
+        return entries[hash];
+    }
+
+};
+
+int main( int argc, char *argv[] ) {
+
+    HashList<float, 13> l;
+
+    l.insert(1024, 2.5f);
+    l.insert(204, 1.5f);
+    l.insert(217, 1.0f);
+
+    printf("1024: %.1f\n", l.find(1024)->elem);
+    printf("204: %.1f\n", l.find(204)->elem);
+    printf("217: %.1f\n", l.find(217)->elem);
+	
+	return 0;
+}