Leetcode ——Partition Equal Subset Sum

Question

Given a non-empty array containing only positive integers, find if the array can be partitioned into two subsets such that the sum of elements in both subsets is equal.

Note:
Each of the array element will not exceed 100.
The array size will not exceed 200.
Example 1:

Input: [1, 5, 11, 5]

Output: true

Explanation: The array can be partitioned as [1, 5, 5] and [11].
Example 2:

Input: [1, 2, 3, 5]

Output: false

Explanation: The array cannot be partitioned into equal sum subsets.

Solution

0-1揹包問題。 dp[j] = dp[j] || dp [j - n];

Code

class Solution {
public:
    bool canPartition(vector<int>& nums) {
        int sum = 0;
        for (int n : nums)
            sum += n;
        if (sum % 2 != 0)
            return false;
        sum /= 2;
        return subsetsum(nums, sum);
    }
    bool subsetsum(vector<int>& nums, int sum) {
        int dp[sum + 1] = {false};
        dp[0] = true;
        for (int i = 0; i < nums.size(); i++) {
            for (int j = sum; j >= nums[i]; j--) {
                dp[j] = dp[j] || dp[j - nums[i]];
            }
        }
        return dp[sum];
    }
};