p303

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LeetCode p303 Range Sum Query - Immutable 题解

1.题目：

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

题意：

输出数组某一段的累加和。

2.解题思路:

累加 做差

3.代码

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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 obj = new NumArray(nums);
 * int param_1 = obj.sumRange(i,j);
 */

4.一些总结：