leetCode -- 三数之和

    var arr = [-1,0,1,2,-1,-4];
    var result = [];
    var obj = {};
    var num = [];
    arr.sort((a,b) => a - b);  //[-4,-1,-1,0,1,2]
    arr.forEach((item,index) => {
      var value = 0 - item;
      var i = 0;
      var j = arr.length-1;
        while(i < j){
          // 如果value大于最大值，小于最小值，在这里面不会有结果
          if(value < arr[i] || value > arr[j]) break;
          else if(value > (arr[i] + arr[j])) i++;
          else if(value < (arr[i] + arr[j])) j--;
          else if(value == (arr[i] + arr[j])){
              if(index != i && index != j){
                var temp = [item,arr[i],arr[j]];
                result.push(temp.sort());
              }
              i ++;
          }
        }
    })

    // 去重
    result.forEach((item,index) => {
      if(!obj[item]){
        num.push(item);
        obj[item] = item;
      }
    })
    console.log(num); // [[-1, -1, 2],[-1, 0, 1]]