Range Sum Query - Immutable(easy)

1.这道题目与pat中的1046. Shortest Distance (20)相类似；

2.使用一个数组dp[i],记录0到第i个数的和

3.求i到j之间的和时，输出dp[j]-dp[i]+num[i]即可。

AC代码如下：

class NumArray {public:    vector<int> dp;    vector<int> num;    NumArray(vector<int> &nums) {        int n=nums.size();        dp=vector<int>(n,0);        num=nums;        for(int i=0;i<n;i++)        {            if(i>0)                dp[i]=dp[i-1]+nums[i];            else                dp[0]=nums[0];        }    }    int sumRange(int i, int j) {        return dp[j]-dp[i]+num[i];    }};// Your NumArray object will be instantiated and called as such:// NumArray numArray(nums);// numArray.sumRange(0, 1);// numArray.sumRange(1, 2);