LeetCode - 416 - Partition Equal Subset Sum

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.

问一个数组能不能划分成和相等的两部分。

可以转化为0/1背包做。先求出数组和，若为奇数，则肯定无法划分，若是偶数sum，则相当于求数组中是否存在子集和 = sum / 2

背包还是两年前跟着连飞学的，居然都过去这么久了，叹气。。。

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