题目

ugly-number-ii

2. 算法

* DP

* dp优化

3. 代码

* dp

class NumArray {
public:
    NumArray(vector<int> &nums) {
        dp = nums;
        for (int i = 1; i < nums.size(); ++i) {
            dp[i] += dp[i - 1];
        }
    }
    int sumRange(int i, int j) {
        return i == 0? dp[j] : dp[j] - dp[i - 1];
    }
private:
    vector<int> dp;
};

* dp优化

class NumArray {
public:
    NumArray(vector<int> &nums) {
        dp.resize(nums.size() + 1, 0);
        for (int i = 1; i <= nums.size(); ++i) {
            dp[i] = dp[i - 1] + nums[i - 1];
        }
    }
    int sumRange(int i, int j) {
        return dp[j + 1] - dp[i];
    }

private:
    vector<int> dp;
};