2018-06-25 23:17:33 +08:00

66 lines
1.8 KiB
C++

// Source : https://leetcode.com/problems/partition-equal-subset-sum/description/
// Author : Hao Chen
// Date : 2018-06-24
/***************************************************************************************
*
* 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.
*
***************************************************************************************/
class Solution {
public:
//back tracking
bool canPartitionRecrusion(vector<int>& nums, int half, int index) {
for (int i=index; i<nums.size(); i++){
int h = half - nums[i];
if ( h < 0 ) return false; //cannot found the solution
if ( h == 0 ) return true; //found the solution
if ( canPartitionRecrusion(nums, h, i+1) == true ) return true;
}
return false;
}
bool canPartition(vector<int>& nums) {
int sum = 0;
for(auto n : nums) sum +=n;
if ( sum & 1 ) return false; // sum % 2 != 1
int half = sum / 2;
//sort the array in descending order
//so, the DFS could be very fast to find the answer because it's greedy.
std::sort(nums.begin(), nums.end(), std::greater<int>());
//go to find a path which sum is half
return canPartitionRecrusion(nums, half, 0);
}
};