MergeSort

Author: fay111101

src/main/java/leetcode/sort/MergeSort.java

@@ -1,74 +1,76 @@
 package leetcode.sort;
 
 public class MergeSort {
-    public void merge(int[] arr,int[] temp,int i,int l1,int l2){
-        int k,j;
-        for(k=i, j=l1+1;i<=l1&&j<=l2; k++){
-            if(arr[i]<=arr[j]){
-                temp[k]=arr[i++];
-            }else{
-                temp[k]=arr[j++];
+    public void merge(int[] arr, int[] temp, int i, int l1, int l2) {
+        int k, j;
+        for (k = i, j = l1 + 1; i <= l1 && j <= l2; k++) {
+            if (arr[i] <= arr[j]) {
+                temp[k] = arr[i++];
+            } else {
+                temp[k] = arr[j++];
             }
         }
-        if(i<=l1){
-            temp[k++]=arr[i++];
+        if (i <= l1) {
+            temp[k++] = arr[i++];
         }
-        if(j<=l2){
-            temp[k++]=arr[j++];
+        if (j <= l2) {
+            temp[k++] = arr[j++];
         }
     }
-    public void mergeSort(int[] arr,int[] result,int start,int end){
-        if(start<end){
-            int m=(start+end)/2;
-            mergeSort(arr,result,start,m);
-            mergeSort(arr,result,m+1,end);
-            merge(arr,result,start,m,end);
+
+    public void mergeSort(int[] arr, int[] result, int start, int end) {
+        if (start < end) {
+            int m = (start + end) / 2;
+            mergeSort(arr, result, start, m);
+            mergeSort(arr, result, m + 1, end);
+            merge(arr, result, start, m, end);
         }
     }
 
-    public static void mergeSort1(int[] arr,int p,int r){
-        if(p<r){
-            int q=(p+r)/2;
-            mergeSort1(arr,p,q);
-            mergeSort1(arr,q+1,r);
-            merge1(arr,p,q,r);
+    public static void mergeSort1(int[] arr, int p, int r) {
+        if (p < r) {
+            int q = (p + r) / 2;
+            mergeSort1(arr, p, q);
+            mergeSort1(arr, q + 1, r);
+            merge1(arr, p, q, r);
 
 
         }
     }
 
-    public static void merge1(int[] arr,int p,int q,int r){
-        int n1=q-p+1;
-        int n2=r-q;
-        int [] arr1=new int [n1+1];
-        int [] arr2=new int [n2+1];
+    public static void merge1(int[] arr, int p, int q, int r) {
+        int n1 = q - p + 1;
+        int n2 = r - q;
+        int[] arr1 = new int[n1 + 1];
+        int[] arr2 = new int[n2 + 1];
 
-        for(int i=0;i<n1;i++){
-            arr1[i]=arr[p+i];
+        for (int i = 0; i < n1; i++) {
+            arr1[i] = arr[p + i];
         }
-        for(int j=0;j<n2;j++){
-            arr2[j]=arr[q+1+j];
+        for (int j = 0; j < n2; j++) {
+            arr2[j] = arr[q + 1 + j];
         }
-        arr1[n1]=Integer.MAX_VALUE;
-        arr2[n2]=Integer.MAX_VALUE;
-        int i=0;
-        int j=0;
-        for(int k=p;k<=r;k++){
-            if(arr1[i]<arr2[j]){
-                arr[k]=arr1[i];
+        arr1[n1] = Integer.MAX_VALUE;
+        arr2[n2] = Integer.MAX_VALUE;
+        int i = 0;
+        int j = 0;
+        for (int k = p; k <= r; k++) {
+            if (arr1[i] < arr2[j]) {
+                arr[k] = arr1[i];
                 i++;
-            }else{
-                arr[k]=arr2[j];
+            } else {
+                arr[k] = arr2[j];
                 j++;
             }
         }
     }
+
     public static void main(String[] args) {
         int[] arr = {49, 38, 65, 97, 76, 13, 27, 49};
-        int[] result=new int[arr.length];
+        int[] result = new int[arr.length];
         MergeSort qs = new MergeSort();
-        qs.mergeSort1(arr, 0, arr.length-1 );
-        qs.mergeSort(arr, result,0, arr.length-1 );
+        qs.mergeSort1(arr, 0, arr.length - 1);
+        qs.mergeSort(arr, result, 0, arr.length - 1);
         for (int num : arr) {
             System.out.println(num);
 

src/main/java/offer/list/MergeTwoSortedList.java

@@ -6,7 +6,7 @@
 public class MergeTwoSortedList {
     public ListNode Merge(ListNode list1, ListNode list2) {
         ListNode p = list1, q = list2;
-        ListNode head = new ListNode(-1);
+        ListNode head = new ListNode(-1);//this is a trick
         ListNode tail = head;
 
         while (p != null && q != null) {