Range Sum query-immutable

Dynamic planning Issues

Given an integer array nums, find the sum of the elements between indices I and J (i ≤ J), inclusive.

Example:

Given nums = [-2, 0, 3, -5, 2, -1]sumrange (0, 2), 1sumRange (2, 5)-1sumrange (0, 5)-3

Note:
   1.assume that thearray does is not a change.
   2.There is many calls to sumrange function.

Personal Summary: See NOTE2 should think this is a dynamic programming problem, each call to calculate will definitely time out, so should be in advance to calculate all the results.
         In addition, some special cases, such as Nuns=[],i or J, may cross the border and should be taken into account.

AC Code Public classnumarray{int[] array,sum;  PublicNumarray (int[] nums) {       if(nums.length==0| | nums==NULL)return; Array=Nums; Sum=Nums; sum[0]=array[0];  for(inti=1;i<array.length;i++) {Sum[i]=sum[i-1]+Array[i]; }  }     Public intSumrange (intIintj) {      if(sum==NULL|| i>j| | J>sum.length)return0; Else {           if(i==0)returnSum[j]; Else          returnSum[j]-sum[i-1]; }    }  }

Range Sum query-immutable