求数组中任意两个数之间所有数字的和

303. Range Sum Query - Immutable

  求数组中任意两个数之间所有数字的和

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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) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

Note:

1. You may assume that the array does not change.
2. There are many calls to sumRange function.

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 1 // 存储数组的结构体
 2 struct NumArray {
 3     int num;
 4     int sum;
 5 };
 6
 7 /** Initialize your data structure here. */
 8 struct NumArray* NumArrayCreate(int* nums, int numsSize) {
 9     int i = 0;
10     struct NumArray *NumArr = (struct NumArray*)malloc(sizeof(struct NumArray)*numsSize);//数组结构体初始化
11     struct NumArray* p = NumArr;
12
13     //非空数组
14     if(numsSize == 0)
15         return NULL;
16
17     //初始化第一个元素
18     p[0].num = nums[0];
19     p[0].sum = nums[0];
20     i++;
21     while(i < numsSize){
22         p[i].num = nums[i];
23         p[i].sum = p[i-1].sum + nums[i];
24         i++;
25     }
26
27     return NumArr;
28 }
29
30 int sumRange(struct NumArray* numArray, int i, int j) {
31     //sum[j] -sum[i] + num[i]
32     return (numArray[j].sum - numArray[i].sum + numArray[i].num);
33 }
34
35 /** Deallocates memory previously allocated for the data structure. */
36 void NumArrayFree(struct NumArray* numArray) {
37     free(numArray);
38 }
39
40 // Your NumArray object will be instantiated and called as such:
41 // struct NumArray* numArray = NumArrayCreate(nums, numsSize);
42 // sumRange(numArray, 0, 1);
43 // sumRange(numArray, 1, 2);
44 // NumArrayFree(numArray);