lintcode-206-区间求和 I

206-区间求和 I

思路

code

/**
* Definition of Interval:
* classs Interval {
*     int start, end;
*     Interval(int start, int end) {
*         this->start = start;
*         this->end = end;
*     }
*/

class SegmentTreeNode2 {
public:
int start, end;
long long sum;
SegmentTreeNode2 *left, *right;
SegmentTreeNode2(int start, int end, long long sum) {
this->start = start;
this->end = end;
this->sum = sum;
this->left = this->right = NULL;
}
};

class Solution {
public:
/*
* @param A: An integer array.
* @param queries: A query list.
* @return: The result list.
*/
vector<long long> intervalSum(vector<int> &A, vector<Interval> &queries) {
// write your code here
if (A.empty() || queries.empty()) {
return vector<long long>();
}

vector<long long> result;
SegmentTreeNode2 * root = build(0, A.size() - 1, A);
for (int i = 0; i < queries.size(); i++) {
result.push_back(query(root, queries[i].start, queries[i].end));
}
return result;
}

SegmentTreeNode2 * build(int start, int end, vector<int> &nums) {
// write your code here
if (start > end) {
return nullptr;
}
SegmentTreeNode2 *root = new SegmentTreeNode2(start, end, 0);
if (start != end) {
root->left = build(start, (start + end) / 2, nums);
root->right = build((start + end) / 2 + 1, end, nums);
root->sum = root->left->sum + root->right->sum;
}
else {
root->sum = nums[start];
}
return root;
}

long long  query(SegmentTreeNode2 *root, int start, int end) {
// write your code here
int mid = (root->start + root->end) / 2;
if (start <= root->start && end >= root->end) {
return root->sum;
}
else if (mid < start) {
return query(root->right, start, end);
}
else if (mid + 1 > end) {
return query(root->left, start, end);
}
else {
return query(root->left, start, mid) + query(root->right, mid + 1, end);
}
}
};