【前缀和】【重点】303.区域和检索-数组不可变

Allenlzcoder

已于 2025-06-18 00:11:26 修改

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分类专栏： labuladong的算法小抄笔记文章标签：前缀和

于 2024-01-02 22:31:19 首次发布

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本文介绍了如何在Java中通过NumArray类实现前缀和算法，包括preSumArray数组的构建和sumRange方法计算指定范围内的和。

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题目

法1：前缀和

参考：灵茶山艾府

Python

class NumArray:

    def __init__(self, nums: List[int]):
        s = [0] * (len(nums) + 1) # s[i]表示nums中前i个数之和
        for i, val in enumerate(nums):
            s[i+1] = s[i] + val
        self.s = s

    def sumRange(self, left: int, right: int) -> int:
        return self.s[right+1] - self.s[left]


# Your NumArray object will be instantiated and called as such:
# obj = NumArray(nums)
# param_1 = obj.sumRange(left,right)

Java

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];
    }
}