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#include "leetcode.h"
struct segNode {
int start, end, sum;
segNode *left, *right;
segNode(int a, int b)
: start(a), end(b), sum(0), left(nullptr), right(nullptr) {}
};
class NumArray {
public:
segNode *root;
NumArray(vector<int> &nums) { root = buildTree(nums, 0, nums.size() - 1); }
void update(int index, int val) { modifyTree(index, val, root); }
int sumRange(int left, int right) { return queryTree(left, right, root); }
private:
segNode *buildTree(vector<int> &nums, int start, int end) {
if (start > end)
return nullptr;
segNode *root = new segNode(start, end);
if (start == end) {
root->sum = nums[start];
return root;
}
int mid = start + (end - start) / 2;
root->left = buildTree(nums, start, mid);
root->right = buildTree(nums, mid + 1, end);
root->sum = root->left->sum + root->right->sum;
return root;
}
int modifyTree(int i, int val, segNode *root) {
if (root == nullptr)
return 0;
int diff;
if (root->start == i && root->end == i) {
diff = val - root->sum;
root->sum = val;
return diff;
}
int mid = (root->start + root->end) / 2;
if (i > mid)
diff = modifyTree(i, val, root->right);
else
diff = modifyTree(i, val, root->left);
root->sum = root->sum + diff;
return diff;
}
int queryTree(int i, int j, segNode *root) {
if (root == nullptr)
return 0;
if (root->start == i && root->end == j)
return root->sum;
int mid = (root->start + root->end) / 2;
if (i > mid)
return queryTree(i, j, root->right);
if (j <= mid)
return queryTree(i, j, root->left);
return queryTree(i, mid, root->left) + queryTree(mid + 1, j, root->right);
}
};
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