给定一个整数数组 nums,求出数组从索引 i 到 j (i ≤ j) 范围内元素的总和,包含 i, j 两点。
示例:
给定 nums = [-2, 0, 3, -5, 2, -1],求和函数为 sumRange()
sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3
说明:
你可以假设数组不可变。
会多次调用 sumRange 方法。
思路:简单版本的动态规划,用一个数组预存nums的和。题目意思不是很明确,需要仔细想想想要表达什么。
typedef struct {
int *numarr;
} NumArray;
NumArray* numArrayCreate(int* nums, int numsSize) {
if(0 == numsSize){
return NULL;
}
NumArray *arr = (NumArray *)calloc(1, sizeof(NumArray));
arr->numarr = (int *)malloc(numsSize * sizeof(int));
memset(arr->numarr, 0x00, numsSize * sizeof(int));
int i = 0;
arr->numarr[0] = nums[0];
for(i = 1; i < numsSize; i++){
arr->numarr[i] = arr->numarr[i - 1] + nums[i];
}
return arr;
}
int numArraySumRange(NumArray* obj, int i, int j) {
if(NULL == obj){
return 0;
}
if(0 == i){
return obj->numarr[j];
}
return obj->numarr[j] - obj->numarr[i - 1];
}
void numArrayFree(NumArray* obj) {
if(NULL != obj){
if(NULL != obj->numarr){
free(obj->numarr);
}
free(obj);
}
}
/**
* Your NumArray struct will be instantiated and called as such:
* struct NumArray* obj = numArrayCreate(nums, numsSize);
* int param_1 = numArraySumRange(obj, i, j);
* numArrayFree(obj);
*/