标签：des style c class blog code
Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Note:
For example, given array S = {1 0 -1 0 -2 2}, and target = 0.
A solution set is:
(-1, 0, 0, 1)
(-2, -1, 1, 2)
(-2, 0, 0, 2)
public class Solution { public ArrayList<ArrayList<Integer>> fourSum(int[] num, int target) { ArrayList<ArrayList<Integer>> re = new ArrayList<ArrayList<Integer>>(); Map<ArrayList<Integer>,Integer> map = new HashMap<ArrayList<Integer>,Integer>(); ArrayList<Integer> ai = new ArrayList<Integer>(); if(num.length<=3) return re; Arrays.sort(num); for(int i=0;i<num.length-3;i++){ ai = new ArrayList<Integer>(); ai.add(num[i]); int tar = target-num[i]; for(int j=i+1;j<num.length-2;j++){ int temp = num[j]; ai = new ArrayList<Integer>(); ai.add(num[i]); ai.add(temp); int tt = tar-temp; int start = j+1; int end = num.length-1; while(end>start){ if(num[start]+num[end]==tt){ ai.add(num[start]); ai.add(num[end]); map.put(ai, 1); ai=new ArrayList<Integer>(); ai.add(num[i]); ai.add(temp); start++; end--; continue; } if(num[start]+num[end]>tt){ end--; continue; } if(num[start]+num[end]<tt){ start++; continue; } } } } re.addAll(map.keySet()); return re; } }
标签：des style c class blog code
原文地址：http://www.cnblogs.com/yixianyixian/p/3746508.html
