LeetCode 416. Partition Equal Subset Sum

原题链接在这里:https://leetcode.com/problems/partition-equal-subset-sum/description/

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:

  1. Each of the array element will not exceed 100.
  2. 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.

题解:

其实是找有没有sub array的数字和是sum/2. Thus for the other half, sum must be sum/2.

Let dp[j] denotes if there is subarray sum equal to j.

dp[0] = true. 

Then for each num in nums, dp[num] would be true.

Thus for j, check if dp[j-num], if dp[j-num] is true. Then dp[j] msut be true. 

Time Complexity: O(sum*nums.length). sum = sum(nums)/2.

Space: O(sum).

AC Java:

 1 class Solution {
 2     public boolean canPartition(int[] nums) {
 3         if(nums == null || nums.length == 0){
 4             return false;
 5         }
 6 
 7         int sum = 0;
 8         for(int num : nums){
 9             sum += num;
10         }
11 
12         if(sum % 2 == 1){
13             return false;
14         }
15 
16         int target = sum / 2;
17         boolean [] dp = new boolean[target + 1];
18         dp[0] = true;
19         for(int num : nums){
20             for(int i = target; i >= num; i--){
21                 dp[i] |= dp[i - num];
22             }
23         }
24 
25         return dp[target];
26     }
27 }

类似Target Sum 的Method 2.

跟上Partition to K Equal Sum Subsets.

posted @ 2017-09-29 02:04  Dylan_Java_NYC  阅读(296)  评论(0编辑  收藏  举报