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#include <vector>

using std::vector;

class NumArray {

public:

NumArray(vector<int>& nums) {

sum = new int[nums.size() + 1]; // 构建前缀和sum，只不过为了方便使用i位置不包含i的前缀和， 给sumRange少一个判断

sum[0] = 0;

for (int i = 1; i < nums.size() + 1; ++i) {

sum[i] = sum[i-1] + nums[i-1];

}

}

int sumRange(int i, int j) {

return sum[j+1] - sum[i];

}

~NumArray() {

if (sum)

delete[] sum;

}

private:

int* sum;

};