leetcode 303. 区域和检索 - 数组不可变

 1 class NumArray {
 2     public int[] prefixSum;
 3     public NumArray(int[] nums) {
 4         prefixSum = new int[nums.length];
 5         prefixSum[0] = nums[0];
 6         for(int i = 1;i < nums.length;i++)
 7             prefixSum[i] = prefixSum[i - 1] + nums[i];
 8     }
 9     
10     public int sumRange(int left, int right) {
11         return left == 0 ? prefixSum[right] : prefixSum[right] - prefixSum[left - 1];
12     }
13 }

引入前缀和的概念就很容易做了

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来源： https://www.cnblogs.com/miracle-zwx/p/15963562.html