几种内排序算法

Posted 2020-07-03 江湖小妞

//直接插入法排序。依次从原来数组中选取元素插入排序后的数组（从后往前找插入位置）
    public static int[] insertSort(int[] nums) {
        if(nums == null || nums.length == 0 || nums.length == 1)
            return nums;
        int temp = 0;
        for(int i=1; i<nums.length; i++) {
            if(nums[i] < nums[i-1]) {
                temp = nums[i];
                int j = i-1;
                do {
                    nums[j+1] = nums[j];
                    j--;
                } while(j >= 0 && nums[j] > temp);
                nums[j+1] = temp;
            }
        }
        return nums;
    }
    
    //折半插入排序，每次寻找插入位置时用二分查找的方法
    public static int[] binaryInsertSort(int[] nums) {
        if(nums == null || nums.length == 0 || nums.length == 1)
            return nums;
        int temp = 0;
        for(int i=1; i<nums.length; i++) {
            if(nums[i] < nums[i-1]) {
                temp = nums[i];
                int low = 0, high = i-1; 
                while(low < high) {
                    int mid = (low + high) / 2;
                    if(temp < nums[mid])
                        high = mid - 1;
                    else
                    low = mid + 1;
                }
                for(int j=i-1; j>=low; j--) 
                    nums[j+1] = nums[j];
                nums[low] = temp;
            }
        }
        return nums;
    }
    
    //希尔排序。每次步长逐渐减小，直至为1.不稳定的算法
    public static int[] shellSort(int[] nums) {
        if(nums == null || nums.length == 0 || nums.length == 1) 
            return nums;
        int i, j, gap = nums.length;
        int temp = 0;
        do {
            gap = gap / 3 + 1;
            for(i=gap; i<nums.length; i++) {
                if(nums[i] < nums[i-gap]) {
                    j = i - gap;
                    temp = nums[i];
                    do {
                        nums[j + gap] = nums[j];
                        j = j - gap;
                    } while(j >= 0 && temp < nums[j]);
                    nums[j+gap] = temp;
                }
            }
        } while(gap > 1);
        return nums;
    }
    
    
    //快速排序。采用分治法，每次选出一个pivot，使得数组左边的元素都比pivot小，数组右边的元素都比pivot大。
    public static void quickSort(int[] nums, int left, int right) {
        if(left < right) {
            int pivotpos = partition(nums, left, right);
            quickSort(nums, left, pivotpos-1);
            quickSort(nums, pivotpos+1, right);
        }
    }
    
    public static int partition(int[] nums, int left, int right) {
        int pivotpos = left, pivot = nums[left];
        for(int i=left+1; i<=right; i++) {
            if(nums[i] < pivot) {
                pivotpos++;
                if(pivotpos != i) {
                    int temp = nums[i];
                    nums[i] = nums[pivotpos];
                    nums[pivotpos] = temp;
                }
            }
        }
        nums[left] = nums[pivotpos];
        nums[pivotpos] = pivot;
        return pivotpos;
    }