303. 区域和检索 - 数组不可变

https://leetcode-cn.com/problems/range-sum-query-immutable/

Java

/*
 * @Author: Goog Tech
 * @Date: 2020-09-15 15:07:30
 * @LastEditTime: 2020-09-15 15:11:43
 * @Description: https://leetcode-cn.com/problems/range-sum-query-immutable/
 * @FilePath: \leetcode-googtech\#303. Range Sum Query - Immutable\Solution.java
 * @Reference: https://leetcode-cn.com/problems/range-sum-query-immutable/solution/marveljian-dan-de-xue-xi-bi-ji-303-by-tyanyonecanc/
 * @WebSite: https://algorithm.show/
 */

class NumArray {

    private int[] sum;

    // DP : 动态规划
    public NumArray(int[] nums) {
        sum = Arrays.copyOf(nums, nums.length);
        for(int i = 1; i < sum.length; i++) {
            // sum[i] 的值为 sum[0] 到 sum[i] 的所有值之和
            sum[i] += sum[i - 1];
        }
    }

    public int sumRange(int i, int j) {
        return (i == 0) ? sum[j] : (sum[j] - sum[i - 1]);
    }
}

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * int param_1 = obj.sumRange(i,j);
 */

Python

'''
Author: Goog Tech
Date: 2020-09-15 15:07:34
LastEditTime: 2020-09-15 15:08:56
Description: https://leetcode-cn.com/problems/range-sum-query-immutable/
FilePath: \leetcode-googtech\#303. Range Sum Query - Immutable\Solution.py
Reference: https://leetcode-cn.com/problems/range-sum-query-immutable/solution/marveljian-dan-de-xue-xi-bi-ji-303-by-tyanyonecanc/
WebSite: https://algorithm.show/
'''

class NumArray(object):

    # DP : 动态规划
    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        if not nums: return
        self.result = [0] * len(nums)
        self.result[0] = nums[0]
        for i in range(1, len(nums)):
            # result[i] 的值为 nums[0] 到 nums[i] 的所有值之和
            self.result[i] = self.result[i - 1] + nums[i]

    def sumRange(self, i, j):
        """
        :type i: int
        :type j: int
        :rtype: int
        """
        if i == 0: return self.result[j]
        else: return self.result[j] - self.result[i - 1]

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