花了两天的时间坐在图书馆里，终于写完了所有主要的数据结构，包括其中的算法部分，呵呵，保研和面试的第一关估计没问题了，下面就是看OS和Network了
心得：纸上得来终觉浅，绝知此事要躬行！当自己回想着算法的整个过程，然后一行一行的敲下来，发现算法太精辟了，看似简单，写起来可真不是那么回事，而且，写多了，熟悉了，思路就快了，写起来就得心应手了！可能你会觉得算法和数据结构对现在的程序员来说已经不重要了，但是，我觉得，好的程序员如果不懂数据结构和算法那么他就写不出更好的代码！作为一个计科男，掌握数据结构和算法是必须的！
好了，下面附上各种排序算法的Java实现，算法的思想不介绍了，网上有很多，如果发现我的代码中有什么错误，也请及时回复我哦！谢谢
1. 冒泡排序
package SortAlgorithm; import java.util.Arrays; /** * 冒泡排序 * * @author yinger */ public class BubbleSort { public static void main(String[] args) { int[] s = new int[] { 10, 23, 43, 9, 25, 87, 56, 34, 11 }; System.out.println("Before: " + Arrays.toString(s));// Before: [10, 23, 43, 9, 25, 87, 56, 34, 11] sort(s);// Arrays.sort(s); System.out.println("After: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] } // bubble sort --- time: O(n^2) public static void sort(int[] s) { int n = s.length; int i, j, temp, flag;// flag: change happened? for (i = n - 1; i >= 1; i--) {// number from end to begin flag = 0; for (j = 0; j < i; j++) {// range is smaller if (s[j] > s[j + 1]) { temp = s[j]; s[j] = s[j + 1]; s[j + 1] = temp; flag = 1; } } if (flag == 0) {// nothing change, sort is done break; } } } }
2. 选择排序
package SortAlgorithm; import java.util.Arrays; /** * 选择排序 * * @author yinger */ public class SelectSort { public static void main(String[] args) { int[] s = new int[] { 10, 23, 43, 9, 25, 87, 56, 34, 11 }; System.out.println("Before: " + Arrays.toString(s));// Before: [10, 23, 43, 9, 25, 87, 56, 34, 11] sort(s);// Arrays.sort(s); System.out.println("After: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] } // select sort --- time: O(n^2) public static void sort(int[] s) { int n = s.length; int i, j, min, minIndex, temp;// minIndex: the index of the min number for (i = 0; i < n - 1; i++) {// every time select the min number minIndex = i; min = s[minIndex]; for (j = i + 1; j <= n - 1; j++) { if (s[j] < min) { minIndex = j; min = s[j]; } } if (minIndex != i) {// only one change temp = s[i]; s[i] = s[minIndex]; s[minIndex] = temp; } } } }
3. 直接插入排序
package SortAlgorithm; import java.util.Arrays; /** * 直接插入排序 * * @author yinger */ public class DirectInsertSort { public static void main(String[] args) { int[] s = new int[] { 10, 23, 43, 9, 25, 87, 56, 34, 11 }; System.out.println("Before: " + Arrays.toString(s));// Before: [10, 23, 43, 9, 25, 87, 56, 34, 11] sort(s);// Arrays.sort(s); System.out.println("After: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] } // direct insert sort --- time: O(n^2) public static void sort(int[] s) { int n = s.length; int i, j, temp; for (i = 1; i < n; i++) {// begin with 1,end with (n-1) temp = s[i]; for (j = i - 1; j >= 0 && s[j] > temp; j--) {// condition: current one (s[i]) is smaller s[j + 1] = s[j];// move back one step } s[j + 1] = temp;// final position:j+1 } } }
4. 折半插入排序
package SortAlgorithm; import java.util.Arrays; /** * 折半插入排序 * * @author yinger */ public class HalfFindInsertSort { public static void main(String[] args) { int[] s = new int[] { 10, 23, 43, 9, 25, 87, 56, 34, 11 }; System.out.println("Before: " + Arrays.toString(s));// Before: [10, 23, 43, 9, 25, 87, 56, 34, 11] sort(s);// Arrays.sort(s); System.out.println("After: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] } // half find insert sort --- time: O(n^2) public static void sort(int[] s) { int n = s.length; int i, j, temp; int low, high, mid; for (i = 1; i < n; i++) {// begin with 1,end with (n-1) temp = s[i]; low = 0; high = i - 1; while (low <= high) {// find the insert position --- low mid = (low + high) / 2; if (s[mid] > temp) { high = mid - 1; } else {// equal in here! equal can be ignored low = mid + 1; } } for (j = i; j > low; j--) {// move back one step s[j] = s[j - 1]; } s[low] = temp; } } }
5. 快速排序
package SortAlgorithm; import java.util.Arrays; /** * 快速排序 * * @author yinger */ public class QuickSort { public static void main(String[] args) { int[] s = new int[] { 10, 23, 43, 9, 25, 87, 56, 34, 11 }; System.out.println("Before: " + Arrays.toString(s));// Before: [10, 23, 43, 9, 25, 87, 56, 34, 11] sort(s);// Arrays.sort(s); System.out.println("After: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] } // quick sort --- time: O(n*log(n)) public static void sort(int[] s) { int n = s.length; subSorrt(s, 0, n - 1); } private static void subSorrt(int[] s, int start, int end) { // System.out.println(" start=" + start + " end=" + end); if (start < end) {// need to sort int low, high, standard; low = start; high = end; standard = s[start];// the standard number while (low < high) { while (low < high && s[high] > standard) {// move high pointer high--; }// end while --> s[high]<standard s[low] = s[high];// s[low] has been saved! --> after this,s[high] has changed to s[low] and saved! low++; while (low < high && s[low] < standard) {// move low pointer low++; }// end while --> s[low]>standard s[high] = s[low]; high--; }// end while if (low > high) { low--;//attention: if low = high,then position is low,but if low > high,then position is high = low-1 } s[low] = standard;// final,end the while loop,standard number should be in (low-1) index // System.out.println(" standard=" + standard + " position=" + low); // System.out.println("Current Array: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] subSorrt(s, start, low - 1);// sort left subSorrt(s, low + 1, end);// sort right }// else do nothing } }
6. 堆排序
package SortAlgorithm; import java.util.Arrays; /** * 堆排序 * * @author yinger */ public class HeapSort { public static void main(String[] args) { int[] s = new int[] { 10, 23, 43, 9, 25, 87, 56, 34, 11 }; System.out.println("Before: " + Arrays.toString(s));// Before: [10, 23, 43, 9, 25, 87, 56, 34, 11] sort(s);// Arrays.sort(s); System.out.println("After: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] } // heap sort --- time: O(n*log(n)) public static void sort(int[] s) { int n = s.length; int last = (n - 2) / 2;// the last node that is not leaf node = the parent of last node is (n-1-1)/2 int i, j, temp;// minIndex = the index of the min node for (i = last; i >= 0; i--) {// first:build a min heap adjustHeap(s, i, n - 1);// then adjust the heap } System.out.println("Build Heap: " + Arrays.toString(s));// Build Heap: [9, 10, 43, 11, 25, 87, 56, 34, 23] for (j = n - 1; j > 0; j--) { temp = s[0];// first:change the start node and the end node s[0] = s[j]; s[j] = temp; adjustHeap(s, 0, j - 1);// after change,adjust the heap System.out.println("Current Heap: " + " j = " + j + " " + Arrays.toString(s)); } } private static void adjustHeap(int[] s, int start, int end) {// adjust the heap from start node to end node int j, l, r, min, minIndex, temp;// minIndex = the index of the min node j = start; temp = s[start];// save it! while (2 * j + 1 <= end) {//2 * j + 1 <= end means in giving range,node j still has child l = 2 * j + 1;// left node r = 2 * j + 2;// right node --- not always exist if (r <= end && s[r] < s[l]) {// find the min node of childe nodes min = s[r];// right node is smaller minIndex = r; } else { min = s[l];// left node is smaller minIndex = l; } if (temp > min) {// parent is bigger,so change! s[j] = min; s[minIndex] = temp; j = minIndex;// change the index of the node,it means the current node has moved to index j } else { break;// if not,break the while loop } } } }
7. 二路归并排序
package SortAlgorithm; import java.util.Arrays; /** * 合并排序 * * @author yinger */ public class MergeSort { public static void main(String[] args) { int[] s = new int[] { 10, 23, 43, 9, 25, 87, 56, 34, 11 }; System.out.println("Before: " + Arrays.toString(s));// Before: [10, 23, 43, 9, 25, 87, 56, 34, 11] sort(s);// Arrays.sort(s); System.out.println("After: " + Arrays.toString(s));// After: [9, 10, 11, 23, 25, 34, 43, 56, 87] } // merge sort --- time: O(n*log(n)) public static void sort(int[] s) { int n = s.length; mergesort(s, 0, n - 1); } private static void mergesort(int[] s, int start, int end) {//merge from start to end if (start < end) { int mid = (start + end) / 2; mergesort(s, start, mid);// sort left mergesort(s, mid + 1, end);// sort right int i = start, j = mid + 1, k, len;// left and right are all sorted,then merge them! len = end - start + 1; int[] temp = new int[len];//use another array to merge for (k = 0; k < len; k++) {// i range (start,mid),and j range (mid+1,end) if ((i <= mid && j <= end && s[i] < s[j]) || j > end) {// if j>end,then copy must copy i temp[k] = s[i]; i++; } else { temp[k] = s[j]; j++; } } for (k = 0; k < len; k++) {// temp is sorted array s[k + start] = temp[k];// copy temp to s } } } }
其他的数据结构内容请看下篇。