segtree general

codes/Segtree-General.cpp

@@ -0,0 +1,73 @@
+//Segtree-General
+//General segree, needs node struct (with members def and epsilon(default) for all of them) and operation lambda (merge)
+
+template <typename T>
+class segtree
+{
+public:
+    // 0 based indexing
+    // def= default value
+    vector<T> t;
+    int n;
+    T def;
+    function<T(T, T)> merge;
+    void build(int _n, T _def, function<T(T, T)> _fx)
+    {
+        n = _n;
+        def = _def;
+        merge = _fx;
+        t.assign(n * 2, def);
+        for (int i = n - 1; i; i--)
+            t[i] = merge(t[i * 2], t[i * 2 + 1]);
+    }
+    void build(vector<T> &a, T _def, function<T(T, T)> _fx)
+    {
+        n = a.size();
+        def = _def;
+        merge = _fx;
+        t.assign(n * 2, def);
+        for (int i = 0; i < n; i++)
+            t[i + n] = T(a[i]);
+        for (int i = n - 1; i; i--)
+            t[i] = merge(t[i * 2], t[i * 2 + 1]);
+    }
+    void update(int i, T v)
+    {
+        for (t[i += n] = T(v); i;)
+        {
+            i /= 2;
+            t[i] = merge(t[i * 2], t[i * 2 + 1]);
+        }
+    }
+    // this query is made on [l, r]
+    T query(int l, int r)
+    {
+        T lans = def, rans = def;
+        for (l += n, r += n + 1; l < r; l /= 2, r /= 2)
+        {
+            if (l % 2)
+                lans = merge(lans, t[l++]);
+            if (r % 2)
+                rans = merge(t[--r], rans);
+        }
+        return merge(lans, rans);
+    }
+};
+
+// demo usage
+struct node
+{
+    int val;
+    node(int x)
+    {
+        val = x;
+    }
+    // default value
+    node()
+    {
+        val = 1e18;
+    }
+};
+
+segtree<node> seg;
+seg.build(n + 1, node(), [&](node x, node y){ return node(min(x.val, y.val)); });