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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// 存储数组的结构体
struct NumArray {
    int num;
    int sum;
};

/** Initialize your data structure here. */
struct NumArray* NumArrayCreate(int* nums, int numsSize) {
    int i = 0;
    struct NumArray *NumArr = (struct NumArray*)malloc(sizeof(struct NumArray)*numsSize);//数组结构体初始化
    struct NumArray* p = NumArr;
   
    //非空数组
    if(numsSize == 0)
        return NULL;
        
    //初始化第一个元素
    p[0].num = nums[0];
    p[0].sum = nums[0];
    i++;
    while(i < numsSize){
        p[i].num = nums[i];
        p[i].sum = p[i-1].sum + nums[i];
        i++;
    }
    
    return NumArr;
}

int sumRange(struct NumArray* numArray, int i, int j) {
    //sum[j] -sum[i] + num[i]
    return (numArray[j].sum - numArray[i].sum + numArray[i].num);
}

/** Deallocates memory previously allocated for the data structure. */
void NumArrayFree(struct NumArray* numArray) {
    free(numArray);
}

// Your NumArray object will be instantiated and called as such:
// struct NumArray* numArray = NumArrayCreate(nums, numsSize);
// sumRange(numArray, 0, 1);
// sumRange(numArray, 1, 2);
// NumArrayFree(numArray);