区域和检索 - 数组可修改

class NumArray {
public:
    void build_segment_tree(vector<int>& value, vector<int>& nums, int pos, int left, int right)
{
	if(left == right)
	{
		value[pos] = nums[left];
		return;
	}
	int mid = (left + right) / 2;
	build_segment_tree(value, nums, pos * 2 + 1, left, mid);
	build_segment_tree(value, nums, pos * 2 + 2, mid + 1, right);
	value[pos] = value[pos * 2 + 1] + value[pos * 2 + 2];
}


//线段树求和
int sum_range_segment_tree(vector<int>& value, int pos, int left, int right, int qleft, int qright)
{
	if(right < qleft || left > qright)
		return 0;
	if(right <= qright && left >= qleft)
		return value[pos];
	int mid = (left + right) / 2;
	return sum_range_segment_tree(value, pos * 2 + 1, left, mid, qleft, qright) + sum_range_segment_tree(value, pos * 2 + 2, mid + 1, right, qleft, qright);
}

//线段树更新
void update_segment_tree(vector<int>& value, int pos, int left, int right, int index, int new_value)
{
	if(left == right && left == index)
	{
		value[pos] = new_value;
		return;
	}
	int mid = (left + right) / 2;
	if(index <= mid)
		update_segment_tree(value, pos * 2 + 1, left, mid, index, new_value);
	else
		update_segment_tree(value, pos * 2 + 2, mid+1, right, index, new_value);

	value[pos] = value[pos * 2 + 1] + value[pos * 2 + 2];
}
    
    NumArray(vector<int> nums) {
        if(nums.size() == 0)
            return;
        int n = nums.size() *4;//一般线段树数组大小是原数组大小的4倍
        for(int i =0;i<n;++i)
            value.push_back(0);
        build_segment_tree(value,nums,0,0,nums.size()-1);
        right_end = nums.size() -1 ;//线段的右端点
    }
    
    void update(int i, int val) {
        update_segment_tree(value,0,0,right_end,i,val);
    }
    
    int sumRange(int i, int j) {
        return sum_range_segment_tree(value,0,0,right_end,i,j);
    }
    
private:
    vector<int> value;
    int right_end;
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * obj.update(i,val);
 * int param_2 = obj.sumRange(i,j);
 */