Lintcode 563. Backpack V

Given n items with size nums[i] which an integer array and all positive numbers. An integer target denotes the size of a backpack. Find the number of possible fill the backpack.

Each item may only be used once

Example

Given candidate items [1,2,3,3,7] and target 7,

A solution set is: 
[7]
[1, 3, 3]

return 2

Code (Java):

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public class Solution {     /**      * @param nums: an integer array and all positive numbers      * @param target: An integer      * @return: An integer      */     public int backPackV(int[] nums, int target) {         if (nums == null || nums.length == 0 || target < 0) {             return 0;         }                   int[] dp = new int[target + 1];         dp[0] = 1;                   for (int i = 1; i <= nums.length; i++) {             for (int j = target; j >= 1; j--) {                 int ans = dp[j];                 if (j - nums[i - 1] >= 0) {                     ans += dp[j - nums[i - 1]];                 }                                   dp[j] = ans;             }         }                   return dp[target];     } }