20190704

code/lc153.java

+package code;
+/*
+ * 153. Find Minimum in Rotated Sorted Array
+ * 题意：反转数组找最小值
+ * 难度：Medium
+ * 分类：Array, Binary Search
+ * 思路：
+ * Tips：边界条件想清楚
+ */
+public class lc153 {
+    public int findMin(int[] nums) {
+        int left = 0;
+        int right = nums.length-1;
+        while(left<right){
+            int mid = (left+right)/2;
+            if(nums[left]<nums[mid]){   //左边有序
+                if(nums[left]<nums[right]){ //在左边找
+                    right = mid-1;
+                }else{
+                    left = mid;
+                }
+            }else{  //右边有序
+                if(nums[right]<nums[mid]){  //边界条件想清楚
+                    left = mid+1;
+                }else{
+                    right = mid;
+                }
+            }
+        }
+        return nums[left];
+    }
+}

code/lc215.java

@@ -6,6 +6,8 @@ package code;
  * 分类：Divide and Conquer, Heap
  * 思路：快排的思想
  * Tips：经典的题目，记一下代码格式，方便快速写出
+ *      两个点 1.降序排序 2.注意等号。 相比快排，省略了首行判断返回 和 交换
+ *      lc912
  */
 public class lc215 {
     public static void main(String[] args) {
@@ -21,10 +23,10 @@ public class lc215 {
         int origin_r = right;
         int cur = nums[left];
         while(left<right) {
-            while (left<right && nums[right] < cur)
+            while (left<right && nums[right] < cur)     //降序排序，方便处理
                 right--;
             nums[left] = nums[right];
-            while (left<right && nums[left] >= cur)
+            while (left<right && nums[left] >= cur) //注意要加个=号，上个while加也行，防止重复数字死循环
                 left++;
             nums[right] = nums[left];
         }

code/lc912.java

+package code;
+/*
+ * 912. Sort an Array
+ * 题意：数组排序
+ * 难度：Medium
+ * 分类：
+ * 思路：
+ * Tips：注意和lc215区别
+ *      lc215
+ */
+public class lc912 {
+    public static void main(String[] args) {
+        int[] arr = sortArray2(new int[]{5,2,3,1});
+        for(int i: arr){
+            System.out.println(i);
+        }
+    }
+
+    // 快排
+    public int[] sortArray(int[] nums) {
+        quickSort(nums, 0, nums.length-1);
+        return nums;
+    }
+    public void quickSort(int[] nums, int left, int right){
+        if(left>=right) return; //注意返回
+        int l = left;
+        int r = right;
+        int pivot = nums[left];
+        while(left<right){
+            while(left<right && nums[right]>=pivot) right--;
+            int temp = nums[right]; nums[right] = nums[left]; nums[left]=temp;  //交换
+            while(left<right && nums[left]<pivot ) left++;
+            temp = nums[right]; nums[right] = nums[left]; nums[left]=temp;
+        }
+        nums[left] = pivot;
+        quickSort(nums, left+1, r);
+        quickSort(nums, l, right-1);
+    }
+
+    // 归并
+    public static int[] sortArray2(int[] nums) {
+        mergeSort(nums, 0, nums.length-1);
+        return nums;
+    }
+    public static void mergeSort(int[] nums, int left, int right){
+        if(left<right) {
+            int mid = (left+right)/2;
+            mergeSort(nums, left, mid);
+            mergeSort(nums, mid+1, right);
+            merge(nums, left, mid, right);
+        }
+    }
+    public static void merge(int[] nums, int left, int mid, int right){
+        int[] temp = nums.clone();  //记住这个方法
+        int cur = left;
+        int pos1 = left;
+        int pos2 = mid+1;
+        while(pos1<=mid && pos2<=right){
+            if(temp[pos1]<temp[pos2]) { //注意是temp 复制后的
+                nums[cur] = temp[pos1];
+                pos1++;
+                cur++;
+            }
+            else {
+                nums[cur] = temp[pos2];
+                pos2++;
+                cur++;
+            }
+        }
+        while(pos1<=mid){
+            nums[cur] = temp[pos1];
+            pos1++;
+            cur++;
+        }
+        while(pos2<=right){
+            nums[cur] = temp[pos2];
+            pos2++;
+            cur++;
+        }
+    }
+}

readme.md

@@ -236,3 +236,5 @@ LeetCode 指南
 | 1026 [Java](./code/lc1026.java)
 | 1027 [Java](./code/lc1027.java)
 | 1028 [Java](./code/lc1028.java)
+| 1093 [Java](./code/lc1093.java)
+| 1094 [Java](./code/lc1094.java)