标签：des style blog io ar color sp for on
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)
1 public class Solution { 2 public List<List<Integer>> fourSum(int[] num, int target) { 3 List<List<Integer>> ret = new ArrayList<List<Integer>>(); 4 if (num==null||num.length<4) return ret; 5 int n=num.length; 6 Arrays.sort(num); 7 int i,j,start,end,sum; 8 for (i = 0; i < n-3; i++) { 9 for (j = i+1; j <n-2 ; j++) { 10 start=j+1; 11 end=n-1; 12 while (start < end) { 13 sum = num[start] + num[end]; 14 if (sum < target - num[i] - num[j]) { 15 start++; 16 }else if (sum > target - num[i] - num[j]) { 17 end--; 18 } else { 19 ArrayList<Integer> list = new ArrayList<Integer>(); 20 list.add(num[i]); 21 list.add(num[j]); 22 list.add(num[start]); 23 list.add(num[end]); 24 ret.add(list); 25 start++; 26 end--; 27 while(end>start && num[start-1]==num[start])++start; 28 while (end>start && num[end+1]==num[end]) --end; 29 } 30 } 31 while (j<n-1&&num[j]==num[j+1]) ++j; 32 33 } 34 while (i<n-1&&num[i]==num[i+1]) ++i; 35 } 36 return ret; 37 } 38 }
标签：des style blog io ar color sp for on
原文地址：http://www.cnblogs.com/birdhack/p/4117524.html
