LeetCode 1480. Running Sum of 1d Array

題目

Input: nums = [1,2,3,4]
Output: [1,3,6,10]
Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4].

解法思維

用foreach()依序相加，再回傳

var runningSum = function(nums) {
    let total=[]
    let sum=0
    nums.forEach(item => {
        sum+=item
        total.push(sum)
    });
    return total
};

用reduce()依序相加，再回傳

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var runningSum = function(nums) {
/*
    The current array index is increamented by the accumlator which is the new value of arr[i]
    
    Example trace:
    
    input:
    [1,2,3,4]
    
        acc i  arr                return value
        0   0  1,2,3,4            0 + 1 = 1
        1   1  1,2,3,4            1 + 2 = 3
        3   2  1,3,3,4            3 + 3 = 6
end  => 6   3  1,3,6,4            6 + 4 = 10
        10  4  1,3,6,10
    
*/
    nums.reduce((acc, _, i, arr) => arr[i] += acc )
    return nums

};