LeetCode学习篇十一——Range Sum Query - Immutable

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

难度：easy 通过率：26.0%
这道题借用一个数组记录从第0项加到第i项的和t[i]，然后在return的时候直接减掉多余的项即可。算法复杂度：O(n)

class NumArray {public:    vector<int> t;    NumArray(vector<int> &nums) {        t = vector<int>(nums.size(), 0);        for(int i = 0; i < nums.size(); i++) {            if(i > 0) t[i] = t[i-1]+nums[i];            else  t[0] = nums[0];        }    }    int sumRange(int i, int j) {        if(i == 0) return t[j];        return t[j]- t[i-1];    }};