设计题——区域和检索
关键词:前缀和
关键思路:要新开辟一个空间,用来保存前缀和(就是累加)。
代码:
typedef struct {
int* sums;
} NumArray;
NumArray* numArrayCreate(int* nums, int numsSize) {
NumArray* ret = (NumArray*)malloc(sizeof(NumArray));
ret->sums = (int*)malloc(sizeof(int) * (numsSize + 1));
ret->sums[0] = 0;
for (int i = 0; i < numsSize; i++) {
ret->sums[i + 1] = ret->sums[i] + nums[i];
}
return ret;
}
int numArraySumRange(NumArray* obj, int left, int right) {
return obj->sums[right + 1] - obj->sums[left];
}
void numArrayFree(NumArray* obj) {
free(obj->sums);
}