[LeetCode][JavaScript]4Sum

 1 /**
 2  * @param {number[]} nums
 3  * @param {number} target
 4  * @return {number[][]}
 5  */
 6 var fourSum = function(nums, target) {
 7     nums = nums.sort(sorting);
 8     var result = [];
 9     var countAppear = {}; twoSumMap = {}, twoSumArr = [];
10     var isFound = new Set();
11     var i, j, twoSum;
12     for(i = 0; i < nums.length; i++){
13         if(!countAppear[nums[i]]){
14             countAppear[nums[i]] = 1;
15         }else{
16             countAppear[nums[i]]++;
17         }
18         for(j = i + 1; j < nums.length; j++){
19             twoSum = nums[i] + nums[j]; 
20             if(!twoSumMap[twoSum]){
21                 twoSumArr.push(twoSum);
22                 twoSumMap[twoSum] = [{small : nums[i], large : nums[j]}];
23             }else if(!arrContains(twoSumMap[twoSum], nums[i], nums[j])){
24                 twoSumMap[twoSum].push({small : nums[i], large : nums[j]});
25             }
26         }
27     }
28     twoSumArr = twoSumArr.sort(sorting);
29     
30     var numA, numB, sum4, tmp, join;
31     for(i = 0, j = twoSumArr.length - 1; i <= j;){
32         numA = twoSumMap[twoSumArr[i]], numB = twoSumMap[twoSumArr[j]];
33         sum4 = twoSumArr[i] + twoSumArr[j];
34         if(sum4 === target){
35             addCandidate(numA, numB, result);
36         }
37         if(sum4 < target){
38             i++;
39         }else{
40             j--;
41         }
42     }
43     return result;
44     
45     function verifyResult(arr){
46         var previous = null, count = 0;
47         for(var i = 0; i < arr.length; i++){
48             if(arr[i] !== previous){
49                 previous = arr[i];
50                 count = 1;
51             }else{
52                 count++;
53                 if(count > countAppear[previous]){
54                     return false;
55                 }
56             }
57         }
58         return true;
59     }
60     function addCandidate(numA, numB, result){
61         var i, j;
62         for(i = 0; i < numA.length; i++){
63             for(j = 0; j < numB.length; j++){
64                 tmp = [numA[i].small, numA[i].large, numB[j].small, numB[j].large];
65                 tmp = tmp.sort(sorting);
66                 if(verifyResult(tmp)){
67                     join = tmp.join(‘#‘);
68                     if(!isFound.has(join)){
69                         isFound.add(join);
70                         result.push(tmp);
71                     }
72                 }            
73             }
74         }
75     }
76     function arrContains(arr, small, large){
77         for(var i = 0; i < arr.length; i++){
78             if(arr[i].small === small && arr[i].large === large){
79                 return true;
80             }
81         }
82         return false;
83     }
84     function sorting(a, b){
85         if(a > b){
86             return 1;
87         }else if(a < b){
88             return -1;
89         }else{
90             return 0;
91         }
92     }
93 };