题目链接

题目描述

思路

直接遍历就好

class NumArray {
    private int[] num;
    public NumArray(int[] nums) {
        this.num = nums;
    }
    public int sumRange(int left, int right) {
        int ant = 0;
        for (int i = left; i <= right; i++) {
            ant += num[i];
        }
        return ant;
    }
}
/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * int param_1 = obj.sumRange(left,right);
 */

优化

没想到还有优化。。。。

class NumArray {
    int[] sums;
    public NumArray(int[] nums) {
        int n = nums.length;
        sums = new int[n + 1];
        for (int i = 0; i < n; i++) {
            sums[i + 1] = sums[i] + nums[i];
        }
    }
    public int sumRange(int i, int j) {
        return sums[j + 1] - sums[i];
    }
}