LINTCODE——区间求和II

LINTCODE——区间求和II

思路：线段树的构造，线段树的查询，线段树的修改的结合版，三个程序拼接再一起就是这个题目的解法了，和统计前面比自己小的数的个数一样

class Solution {class SegmentTreeNode{ public:      int start, end;      long long count;      SegmentTreeNode *left, *right;      SegmentTreeNode(int start, int end, int count) {          this->start = start;          this->end = end;          this->count = count;          this->left = this->right = NULL;      } };private:    SegmentTreeNode *root;public:    /* you may need to use some attributes here */    /*    * @param A: An integer array    */    Solution(vector<int> A) {        // do intialization if necessary        root = build(0,A.size()-1);        for(int i = 0; i<A.size(); i++)        {            modify(i, A[i]);        }    }    /*     * @param start: An integer     * @param end: An integer     * @return: The sum from start to end     */    long long query(int start, int end) {        // write your code here        return query(root, start, end);    }    long long query(SegmentTreeNode *root, int start, int end)    {        if(root == NULL || start > end)            return 0;        if(start <= root -> start && end >= root -> end)            return root -> count;        int mid = (root -> start + root -> end)/2;        if(start > mid)            return query(root -> right , start, end);        else if(end < mid +1)            return query(root -> left ,start ,end);        else            return( query(root->left, start ,mid) + query(root -> right , mid +1,end) );    }    /*     * @param index: An integer     * @param value: An integer     * @return: nothing     */    void modify(int index, int value) {        // write your code here        modify(root, index, value);    }    void modify(SegmentTreeNode *root, int index, int value)    {        if(root == NULL || index < root -> start || index > root -> end)            return;        if(root->start == index && root -> end == index)        {            root -> count = value;            return;        }        else        {            int mid = (root -> start + root -> end)/2;            if(index > mid )                modify(root->right, index, value);            else                 modify(root->left, index, value);        }        //root的值等于左节点加右节点        root -> count = root->left->count + root->right->count;        return;    }    SegmentTreeNode *build(int start, int end) {        // write your code here        if(start > end)            return NULL;        SegmentTreeNode *root = new SegmentTreeNode(start,end,0);        if(start == end)        {            root->left = root -> right = NULL;            return root;        }            root->left = build(root->start,(root->start+root->end)/2);        root->right= build((root->start+root->end)/2+1 , root -> end);        return root;    }};