LeetCode 307. Range Sum Query - Mutable

Posted on Edited on In 
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const int N = 30001;
int tree[N << 2];
class NumArray {
private:
    vector<int> nums;
    int n;
    void build(int p, int l, int r) {
        if (l == r) {
            tree[p] = nums[l - 1];
            return;
        }
        int m = l + r >> 1;
        build(p * 2, l, m), build(p * 2 + 1, m + 1, r);
        tree[p] = tree[p * 2] + tree[p * 2 + 1];
    }
    int query(int p, int l, int r, int i, int j) {
        if (i <= l && r <= j) return tree[p];
        int m = l + r >> 1, s = 0;
        if (i <= m) s += query(p * 2, l, m, i, j);
        if (j > m) s += query(p * 2 + 1, m + 1, r, i, j);
        return s;
    }
    void update(int p, int l, int r, int i, int v) {
        if (l == r) {
            tree[p] = v;
            return;
        }
        int m = l + r >> 1;
        if (i <= m) update(p * 2, l, m, i, v);
        else update(p * 2 + 1, m + 1, r, i, v);
        tree[p] = tree[p * 2] + tree[p * 2 + 1];
    }
public:
    NumArray(vector<int>& nums) {
        this->nums = nums;
        this->n = nums.size();
        memset(tree, 0, (n + 1) * 8);
        build(1, 1, n);
    }
    
    void update(int index, int val) {
        update(1, 1, n, index + 1, val);
    }
    
    int sumRange(int left, int right) {
        return query(1, 1, n, left + 1, right + 1);
    }
};
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const int N = 30001;
int c[N];
class NumArray {
private:
    vector<int> nums;
    int n;
    void build() {
        for (int i = 0; i < n; ++i) {
            // add(i + 1, nums[i]);
            c[i + 1] += nums[i];
            int j = i + lowbit(i);
            if (j <= n)
                c[j] += c[i];
        }
    }
    int lowbit(int x) {
        return x & -x;
    }
    void add(int i, int k) {
        while (i <= n) {
            c[i] += k;
            i += lowbit(i);
        }
    }
    int query(int i) {
        int s = 0;
        while (i > 0) {
            s += c[i];
            i -= lowbit(i);
        }
        return s;
    }
public:
    NumArray(vector<int>& nums) {
        this->nums = nums;
        this->n = nums.size();
        memset(c, 0, (n + 1) * 4);
        build();
    }
    
    void update(int index, int val) {
        add(index + 1, val - nums[index]);
        nums[index] = val;
    }
    
    int sumRange(int left, int right) {
        return query(right + 1) - query(left);
    }
};