题目

法1：前缀和

class NumArray {private int[] preSumArray;public NumArray(int[] nums) {preSumArray = new int[nums.length + 1];for (int i = 1; i < nums.length + 1; ++i) {preSumArray[i] = preSumArray[i - 1] + nums[i - 1];}}public int sumRange(int left, int right) {return preSumArray[right + 1] - preSumArray[left];}
}