力扣每日一题 区域和检索 - 数组不可变 前缀和

Problem: 303. 区域和检索 - 数组不可变

时间复杂度: $O(n)$

空间复杂度:$O(n)$

Code

class NumArray {

    int[] s;
    public NumArray(int[] nums) {
        int n = nums.length;
        s  = new int[n + 1];
        for(int i = 1; i <= n; i++)
            s[i] = s[i-1] + nums[i-1];
    }
    
    public int sumRange(int l, int r) {
        return s[r+1] - s[l];
    }
}

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