手撕代码-基础排序算法

0.交换元素方法

        private void Swap(ref int a, ref int b) {
            var temp = a;
            a = b;
            b = temp;
        }

1.冒泡排序

        public int[] BubbleSort(int[] originInts) {
            if (originInts == null || originInts.Length == 0) {
                return null;
            }
            int length = originInts.Length;
            for (int i = 0; i < length - 1; i++) {
                for (int j = i + 1; j < length; j++) {
                    if (originInts[i] > originInts[j]) {
                        Swap(ref originInts[i], ref originInts[j]);
                    }
                }
            }
            return originInts;
        }

2.快速排序

步骤①选中枢点②排序并返回中枢点③给字段排序

        public int[] QuickSort(int[] originInts) {
            if (originInts == null || originInts.Length == 0) {
                return null;
            }
            int length = originInts.Length;
            SubQuickSort(originInts, 0, length - 1);
            return originInts;
        }

        private void SubQuickSort(int[] originInts, int leftIndex, int rightIndex) {
            if (leftIndex > rightIndex) {
                return;
            }
            int partitionIndex = SortAndPartition(originInts, leftIndex, rightIndex);
            SubQuickSort(originInts, leftIndex, partitionIndex - 1);
            SubQuickSort(originInts, partitionIndex + 1, rightIndex);
        }

        private int SortAndPartition(int[] originInts, int leftIndex, int rightIndex) {
            int p = leftIndex;
            int q = rightIndex;
            int pivotValue = originInts[rightIndex];//对比锚点为队尾，此时队头的哨兵先移动
            while (p != q) {//终止的条件为两哨兵相遇，此时与锚点交换位置
                while (originInts[p] <= pivotValue && p < q) {//队头哨兵找到第一个比锚点大的点
                    p++;
                }
                while (originInts[q] >= pivotValue && p < q) {//队尾哨兵找到第一个比锚点小的点或者遇到了队头哨兵
                    q--;
                }
                if (p < q) {//两哨兵还没有相遇，交换数据之后继续向对方探测
                    Swap(ref originInts[p], ref originInts[q]);
                }
            }
            //完成第一次排序
            Swap(ref originInts[p], ref originInts[rightIndex]);
            return p;
        }