歸並排序算法

歸並排序：利用分而治之的思想。

歸並排序代碼

public static void merge(int[] arr, int left, int mid, int right){
    int[] temp = new int[right - left + 1]; //新開一個臨時數組存放每一代gap排好序的數組
    int i = left, j = mid + 1, k = 0;
    while (i <= mid && j <= right){
        if (arr[i] < arr[j]){
            temp[k++] = arr[i++];
 
        }else{
            temp[k++] = arr[j++];
        }
    }

    while (i <= mid){
        temp[k++] = arr[i++];
    }

    while (j <= right){
        temp[k++] = arr[j++];
    }

    for (int x = 0; x < k; x++){
        arr[left+x] = temp[x];
    }
}

public static void mergeSort(int arr[], int left, int
 
 right){
    if (left < right){
        int mid = (left + right) / 2;
        mergeSort(arr, left, mid);
        mergeSort(arr, mid+1, right);
        merge(arr, left, mid, right);
    }
}

測試樣例

int[] arr = {2, 4, 9, 3, 8, 6, 7, 1, 5};
mergeSort(arr, 0, 8);
    for (int x : arr){
    System.out.print(x + " "
 
);
}

結果：

1 2 3 4 5 6 7 8 9 

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07-歸並排序算法