题目：

题解：

typedef struct {int* pre;int preSize;int total;
} Solution;Solution* solutionCreate(int* w, int wSize) {Solution* obj = malloc(sizeof(Solution));obj->pre = malloc(sizeof(int) * wSize);obj->preSize = wSize;obj->total = 0;for (int i = 0; i < wSize; i++) {obj->total += w[i];if (i > 0) {obj->pre[i] = obj->pre[i - 1] + w[i];} else {obj->pre[i] = w[i];}}return obj;
}int binarySearch(Solution* obj, int x) {int low = 0, high = obj->preSize - 1;while (low < high) {int mid = (high - low) / 2 + low;if (obj->pre[mid] < x) {low = mid + 1;} else {high = mid;}}return low;
}int solutionPickIndex(Solution* obj) {int x = rand() % obj->total + 1;return binarySearch(obj, x);
}void solutionFree(Solution* obj) {free(obj->pre);free(obj);
}