canPartition.cpp

class Solution {
public:
    bool canPartition(vector<int>& nums) {
        int sum = accumulate(nums.begin(), nums.end(), 0), target = sum >> 1;
        if (sum & 1) return false;
        vector<bool> dp(target + 1, 0);
        dp[0] = true;
        for(auto num : nums)
            for(int i = target; i >= num; i--)
                dp[i] = dp[i] || dp[i - num];
        return dp[target];
    }
};


class Solution {
public:
    bool canPartition(vector<int>& nums) {
        const int MAX_NUM = 100;
        const int MAX_ARRAY_SIZE = 200;
        bitset<MAX_NUM * MAX_ARRAY_SIZE / 2 + 1> bits(1);
        int sum = 0;
        for (auto n : nums) {
            sum += n;
            bits |= bits << n;  //moving everybit to left  n bits means all possible pre sum has been added with n
        }
        return !(sum % 2) && bits[sum / 2];
    }
};