三路歸并算法的關鍵在于分割點的下標計算 package fenzhi;public class MergeSortTest { public static void main(String[] args) { int[] data = new int[] { 5, 3, 6, 2, 16, 9, 4, 5, 3, 6, 2, 16, 9, 4, 7,10,11,15, 8,12,13,1,14,7,10,11,15, 8,12,13,1,14, 5, 3, 6, 2, 16, 9, 4, 7,10,11,15, 8,12,13,1,14}; print(data); mergeSort(data); System.out.println("排序后的數組："); print(data); } public static void mergeSort(int[] data) { sort(data,0,data.length -1); } public static void sort(int[] data, int left, int right) { if (left >= right) return; // 找出中間索引 int center_first = left+((right-left)/3); int center_next=right-(right-left)/3;// 對左邊1/3數組進行遞歸 sort(data, left, center_first);// 對中間1/3數組進行遞歸 sort(data, center_first + 1, center_next);// 對右側1/3數組進行遞歸 sort(data,center_next+ 1, right);// 合并 merge(data, left, center_first,center_next, right);print(data); } public static void merge(int[] data, int left, int center_first,int center_next, int right) { // 臨時數組 int[] tmpArrList = new int[data.length]; // 三段數組的三個起點int first=left;int second = center_first+1; int third=center_next+1;//臨時數組的起點 int num=left;int tmp=left;while (first <= center_first && second<=center_next&&third <= right) { // 從三個數組中取出最小的放入臨時數組 if (data[first] <= data[second]&&data[first]<=data[third]) { tmpArrList[num] = data[first];first++;num++;} else if(data[second] <= data[first]&&data[second]<=data[third]){tmpArrList[num] = data[second];second++;num++;}else { tmpArrList[num] = data[third];third++;num++;} } // 當有一個數組率先全部排進臨時數組后，繼續排剩下的兩個數組while (first <= center_first&&second<=center_next) { if (data[first] <= data[second]) { tmpArrList[num] = data[first];first++;num++;} else{tmpArrList[num] = data[second];second++;num++;}} while (second <= center_next&&third<=right) { if (data[second] <= data[third]) { tmpArrList[num] = data[second];second++;num++;} else{tmpArrList[num] = data[third];third++;num++;}} while (first <= center_first&&third<=right) { if (data[first] <= data[third]) { tmpArrList[num] = data[first];first++;num++;} else{tmpArrList[num] = data[third];third++;num++;}} //當兩個數組全部排進臨時數組后，只剩下一個數組while (first <= center_first){tmpArrList[num] = data[first];first++;num++;}while (second <= center_next){tmpArrList[num] = data[second];second++;num++;}while(third<=right){tmpArrList[num] = data[third];third++;num++;}// 將臨時數組中的內容拷貝回原數組中 // （原left-right范圍的內容被復制回原數組） while (tmp <=right) { data[tmp] = tmpArrList[tmp];tmp++;} } public static void print(int[] data) { for (int i = 0; i < data.length; i++) { System.out.print(data[i] + " "); } System.out.println();} }

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