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## Average pair

### 兩數相加平均數

• 必須是被排序好的
• 應用在找尋有哪些配對符合所要的數值
接下來讓我們實作吧!!!

#### 迴圈版BigO(n^2)

``````let array1 = [-11,0,1,2,3,4,5,6,7,8]
let iunputavg = 2

function Average(array, avg){
let result = []
for(let i = 0; i < array.length -1; i++){
for(let j = 1; j < array.length -1; j++){ //index0已經當root了 所以j從index1開始即可
if((array[i] + array[j]) /2 === avg){ //相加/2 === avg
result.push([array[i],array[j]])
}
}
}return result
}
console.log(Average(array1, iunputavg))//[ [ 0, 4 ], [ 1, 3 ], [ 2, 2 ], [ 3, 1 ], [ 4, 0 ] ]

``````

#### Pointer BigO(n)

``````let array1 = [-11,0,1,2,3,4,5,6,7,8]
let iunputavg = 2

function AveragePointer(array, avg){
let left = 0
let right = array.length -1
let result = []

while(array[right] > array[left]){ //當index[i] > index[i-1] = true才執行
if(((array[right] + array[left]) /2) > avg){
right --    //若大於目標值 代表右邊範圍過大 right -1
}else if(((array[right] + array[left]) /2) < avg){
left ++     //若小於目標值 代表左邊範圍過大 left +1
}
else{ //若都符合push result
result.push([array[right],array[left]])
right-- //由於已經成功所以要縮小範圍
left++  //由於已經成功所以要縮小範圍
}
}return result
}
console.log(AveragePointer(array1, iunputavg)) //[ [ 4, 0 ], [ 3, 1 ] ]

``````