Leetcode 416. Partition Equal Subset Sum[medium]

题目：
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.

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一道大水题，做了好久。
vector bool性能存才很大的问题，一直tle。
貌似这个东西不是个容器。

dp[i][j]表示前i个数字差为j是否可达，转移方程很显然，就不多说了。
使用滚动数组压缩空间。

class Solution {
public:
    bool canPartition(vector<int>& nums) {
        int n = nums.size();
        int sum = 0;
        for (int i = 0; i < n; i++) sum += nums[i];
        vector<int> dp[2];// cannot bool??????why????
        dp[0].resize(sum + 1);
        dp[1].resize(sum + 1);
        dp[0][nums[0]] = true;
        for (int i = 1; i < n; i++) {
            for (int j = 0; j <= sum; j++) {
                dp[i & 1][j] = false;
                if (dp[(i - 1) & 1][tabs(j - nums[i])]) dp[i & 1][j] = true;
                if (j + nums[i] <= sum && dp[(i - 1) & 1][j + nums[i]]) dp[i & 1][j] = true;
                //cout << i << "   " << j << "    " << dp[i & 1][j] << endl;
            }
        } 
        return dp[(n - 1) & 1][0];
    }
};