(Leetcode)377. Combination Sum IV (medium)

Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.
Example:
nums = [1, 2, 3]
target = 4

The possible combination ways are:
(1, 1, 1, 1)
(1, 1, 2)
(1, 2, 1)
(1, 3)
(2, 1, 1)
(2, 2)
(3, 1)

Note that different sequences are counted as different combinations.

Therefore the output is 7.

其实这道题目就是爬楼梯的变形，不同的是每次能走的步数由一个int向量给出来，因此上一步的楼层数得减去向量中每一个值（得包含比较大小的过程，用于初始化初始条件，同时对目标值为0的方案书赋值为1，以便当target等于向量中的某一个值时至少有一种走法）

我的答案：

class Solution {
public:
    int combinationSum4(vector<int>& nums, int target) {
        int sum[100000] = {};
        sum[0] = 1;
        for (int i = 0; i <= target; i++) {
            for (int j = 0; j < nums.size(); j++) {
                if (i >= nums[j]) {
                    sum[i] += sum[i - nums[j]];
                }
            }
        }
        return sum[target];
    }
};