initialize repository of algorithm-template

segment-tree/segment-tree.cpp

@@ -0,0 +1,41 @@
+#include <vector>
+
+class SegmentTree {
+private:
+	vector<int> segVal;
+	void maintain(int node) {
+		segVal[node] = max(segVal[node * 2], segVal[node * 2 + 1]);
+	}
+	void build(const vector<int>& vec, int node, int left, int right) {
+		if (left == right) {
+			segVal[node] = vec[left];
+			return;
+		}
+		int mid = (left + right) / 2;
+		build(vec, node * 2, left, mid);
+		build(vec, node * 2 + 1, mid + 1, right);
+		maintain(node);
+	}
+public:
+	SegmentTree(const vector<int>& vec) {
+		size_t n = vec.size();
+		segVal.resize(2 << std::bit_width(n - 1));
+		build(vec, 1, 0, n - 1);
+	}
+	int findFirstAndUpdate(int node, int left, int right, int val) {
+		if (segVal[node] < val) {
+			return -1;	// not found;
+		}
+		if (left == right) {
+			segVal[node] = -1;	// update state
+			return left;
+		}
+		int mid = (left + right) / 2;
+		int idx = findFirstAndUpdate(node * 2, left, mid, val);
+		if (idx < 0) {
+			idx = findFirstAndUpdate(node * 2 + 1, mid + 1, right, val);
+		}
+		maintain(node);
+		return idx;
+	}
+};