LeetCode "Range Sum Query - Mutable"

標籤：

Fenwick tree can do this job.

class NumArray {    vector<int> in;    vector<int> ft;    int query(int i)    {         i += 1;        i = min(i, int(ft.size() - 1));        int s = 0;          for (; i > 0; i -= (i & -i))             s += ft[i];          return s;     }    void init(int i, int v) {    i += 1;    for (; i < ft.size(); i += (i & -i))            ft[i] += v;    }public:    NumArray(vector<int> &nums) {    in = nums;        int n = nums.size();    ft.assign(n + 1, 0);    for(int i = 0; i < n; i ++)        init(i, nums[i]);    }    void update(int i, int v) {    int d = v - in[i];    in[i] = v;    i += 1;    for (; i < ft.size(); i += (i & -i))            ft[i] += d;    }    int sumRange(int i, int j) {        return query(j) - (i ? query(i - 1) : 0);    }};

LeetCode "Range Sum Query - Mutable"