C# 实现LeetCode 307. 区域和检索 - 数组可修改

public class NumArray
{
    public interface Merger<T>
    {
        T morge(T a, T b);

    }

    public class SegmentTree<T>
    {
        private T[] data;
        public T[] tree;
        private Merger<T> merger;
        public SegmentTree(T[] arr, Merger<T> merger)
        {
            this.merger = merger;
            data = new T[arr.Length];
            for (var i = 0; i < arr.Length; i++)
            {
                data[i] = arr[i];
            }
            tree = new T[4 * arr.Length];
            buildSegmentTree(0, 0, data.Length - 1);
        }

        private void buildSegmentTree(int treeindex, int l, int r)
        {
            if (l == r)
            {
                tree[treeindex] = data[l];
                return;
            }
            int leftTreeIndex = leftChild(treeindex);
            int rightTreeIndex = rightChild(treeindex);
            int mid = l + (r - l) / 2;
            buildSegmentTree(leftTreeIndex, l, mid);
            buildSegmentTree(rightTreeIndex, mid + 1, r);

            tree[treeindex] = merger.morge(tree[leftTreeIndex], tree[rightTreeIndex]);

        }

        public int getSize()
        {
            return data.Length;
        }
        public T get(int index)
        {
            if (index < 0 || index >= data.Length)
                throw new System.Exception("Index illegal");
            return data[index];
        }
        public int leftChild(int index)
        {
            return 2 * index + 1;

        }
        public int rightChild(int index)
        {
            return 2 * index + 2;
        }
        public override string ToString()
        {

            System.Text.StringBuilder stringBuilder = new System.Text.StringBuilder();
            stringBuilder.Append('[');
            for (var i = 0; i < tree.Length; i++)
            {
                if (tree[i] != null)
                {
                    stringBuilder.Append(tree[i]);
                }
                else
                {
                    stringBuilder.Append("null");
                }
                stringBuilder.Append(",");
            }
            stringBuilder.Append("]");
            return stringBuilder.ToString();
        }
        /// <summary>
        /// 返回区间 【queryL queryR】的值
        /// </summary>
        /// <param name="queryl"></param>
        /// <param name="queryR"></param>
        /// <returns></returns>
        public T query(int queryl, int queryR)
        {
            if (queryl < 0 || queryl >= data.Length || queryR < 0 || queryR >= data.Length || queryl > queryR)
                throw new System.Exception("index is illegil");
            return query(0, 0, data.Length - 1, queryl, queryR);
        }
        private T query(int treeindex, int l, int r, int queryl, int queryR)
        {
            if (l == queryl && r == queryR)
            {
                return tree[treeindex];
            }
            int mid = l + (r - l) / 2;
            int leftIndex = leftChild(treeindex);
            int rightIndex = rightChild(treeindex);
            if (queryl >= mid + 1)
            {
                return query(rightIndex, mid + 1, r, queryl, queryR);
            }
            else if (queryR <= mid)
            {
                return query(leftIndex, l, mid, queryl, queryR);
            }
            T leftResult = query(leftIndex, l, mid, queryl, mid);
            T rightResult = query(rightIndex, mid + 1, r, mid + 1, queryR);
            return merger.morge(leftResult, rightResult);
        }
        public void set(int index, T data)
        {
            if (index < 0 || index >= this.data.Length)
            {
                throw new System.Exception(" index is illegal");
            }
            set(0, 0, this.data.Length - 1, index, data);
        }
        private void set(int treeIndex, int l, int r, int index, T data)
        {
            if (l == r)
            {
                tree[treeIndex] = data;
                return;
            }
            int mid = l + (r - l) / 2;
            int leftTreeIndex = leftChild(treeIndex);
            int rightTreeIndex = rightChild(treeIndex);
            if (index >= mid + 1)
            {
                set(rightTreeIndex, mid + 1, r, index, data);
            }
            else
            {
                set(leftTreeIndex, l, mid, index, data);
            }
            tree[treeIndex] = merger.morge(tree[leftTreeIndex], tree[rightTreeIndex]);
        }
    }
    class MyMerger<T> : Merger<T>
    {
        public T morge(T a, T b)
        {
            dynamic v1 = a;
            dynamic v2 = b;
            return (T)(v1 + v2);
        }
    }
    SegmentTree<int> tree;
    public NumArray(int[] nums)
    {
        tree = new SegmentTree<int>(nums, new MyMerger<int>());
    }

    public void Update(int index, int val)
    {
        if (tree == null) throw new System.Exception("....");
        tree.set(index, val);
    }

    public int SumRange(int left, int right)
    {
        if (tree == null) throw new System.Exception("....");
        return tree.query(left, right);
    }
}

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * obj.Update(index,val);
 * int param_2 = obj.SumRange(left,right);
 */