Java [Leetcode 303]Range Sum Query - Immutable

Posted 2020-06-14

题目描述：

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Example:

Given nums = [-2, 0, 3, -5, 2, -1]

sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

 

Note:

1. You may assume that the array does not change.
2. There are many calls to sumRange function.

解题思路：

如代码所示。

代码如下：

public class NumArray {
	int[] nums;

    public NumArray(int[] nums) {
        for(int i = 1; i < nums.length; i++){
        	nums[i] += nums[i - 1];
        }
        this.nums = nums;
    }

    public int sumRange(int i, int j) {
        if(i == 0)
        	return nums[j];
        return nums[j] - nums[i - 1];
    }
}


// Your NumArray object will be instantiated and called as such:
// NumArray numArray = new NumArray(nums);
// numArray.sumRange(0, 1);
// numArray.sumRange(1, 2);