Merge branch 'youngyangyang04:master' into master

Author: hailincai

problems/0037.解数独.md

@@ -293,85 +293,40 @@ class Solution:
         """
         Do not return anything, modify board in-place instead.
         """
-        def backtrack(board):
-            for i in range(len(board)):  #遍历行
-                for j in range(len(board[0])):  #遍历列
-                    if board[i][j] != ".": continue
-                    for k in range(1,10):  #(i, j) 这个位置放k是否合适
-                        if isValid(i,j,k,board):
-                            board[i][j] = str(k)  #放置k
-                            if backtrack(board): return True  #如果找到合适一组立刻返回
-                            board[i][j] = "."  #回溯，撤销k
-                    return False  #9个数都试完了，都不行，那么就返回false
-            return True  #遍历完没有返回false，说明找到了合适棋盘位置了
-        def isValid(row,col,val,board):
-            for i in range(9):  #判断行里是否重复
-                if board[row][i] == str(val):
-                    return False
-            for j in range(9):  #判断列里是否重复
-                if board[j][col] == str(val):
-                    return False
-            startRow = (row // 3) * 3
-            startcol = (col // 3) * 3
-            for i in range(startRow,startRow + 3):  #判断9方格里是否重复
-                for j in range(startcol,startcol + 3):
-                    if board[i][j] == str(val):
-                        return False
-            return True
-        backtrack(board)
-```
-
-Python3:
-
-```python3
-class Solution:
-    def __init__(self) -> None:
-        self.board = []
-
-    def isValid(self, row: int, col: int, target: int) -> bool:
-        for idx in range(len(self.board)):
-            # 同列是否重复
-            if self.board[idx][col] == str(target):
+        self.backtracking(board)
+
+    def backtracking(self, board: List[List[str]]) -> bool:
+        # 若有解，返回True；若无解，返回False
+        for i in range(len(board)): # 遍历行
+            for j in range(len(board[0])):  # 遍历列
+                # 若空格内已有数字，跳过
+                if board[i][j] != '.': continue
+                for k in range(1, 10):  
+                    if self.is_valid(i, j, k, board):
+                        board[i][j] = str(k)
+                        if self.backtracking(board): return True
+                        board[i][j] = '.'
+                # 若数字1-9都不能成功填入空格，返回False无解
                 return False
-            # 同行是否重复
-            if self.board[row][idx] == str(target):
+        return True # 有解
+
+    def is_valid(self, row: int, col: int, val: int, board: List[List[str]]) -> bool:
+        # 判断同一行是否冲突
+        for i in range(9):
+            if board[row][i] == str(val):
                 return False
-            # 9宫格里是否重复
-            box_row, box_col = (row // 3) * 3 + idx // 3, (col // 3) * 3 + idx % 3
-            if self.board[box_row][box_col] == str(target):
+        # 判断同一列是否冲突
+        for j in range(9):
+            if board[j][col] == str(val):
                 return False
+        # 判断同一九宫格是否有冲突
+        start_row = (row // 3) * 3
+        start_col = (col // 3) * 3
+        for i in range(start_row, start_row + 3):
+            for j in range(start_col, start_col + 3):
+                if board[i][j] == str(val):
+                    return False
         return True
-    
-    def getPlace(self) -> List[int]:
-        for row in range(len(self.board)):
-            for col in range(len(self.board)):
-                if self.board[row][col] == ".":
-                    return [row, col]
-        return [-1, -1]
-    
-    def isSolved(self) -> bool:
-        row, col = self.getPlace() # 找个空位置
-        
-        if row == -1 and col == -1: # 没有空位置，棋盘被填满的
-            return True
-        
-        for i in range(1, 10):
-            if self.isValid(row, col, i): # 检查这个空位置放i，是否合适
-                self.board[row][col] = str(i) # 放i
-                if self.isSolved(): # 合适，立刻返回, 填下一个空位置。
-                    return True
-                self.board[row][col] = "." # 不合适，回溯
-        
-        return False # 空位置没法解决
-
-    def solveSudoku(self, board: List[List[str]]) -> None:
-        """
-        Do not return anything, modify board in-place instead.
-        """
-        if board is None or len(board) == 0:
-            return
-        self.board = board
-        self.isSolved()
 ```
 
 Go：

problems/0337.打家劫舍III.md

@@ -368,6 +368,41 @@ class Solution:
         return (val1, val2)
 ```
 
+Go:
+
+> 动态规划
+
+```go
+func rob(root *TreeNode) int {
+	res := robTree(root)
+	return max(res[0], res[1])
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func robTree(cur *TreeNode) []int {
+	if cur == nil {
+		return []int{0, 0}
+	}
+	// 后序遍历
+	left := robTree(cur.Left)
+	right := robTree(cur.Right)
+
+    // 考虑去偷当前的屋子
+	robCur := cur.Val + left[0] + right[0]
+    // 考虑不去偷当前的屋子
+	notRobCur := max(left[0], left[1]) + max(right[0], right[1])
+
+    // 注意顺序：0:不偷，1:去偷
+	return []int{notRobCur, robCur}
+}
+```
+
 JavaScript：
 
 > 动态规划

problems/0416.分割等和子集.md

@@ -226,6 +226,32 @@ class Solution:
         return taraget == dp[taraget]
 ```
 Go：
+```go
+// 分割等和子集 动态规划
+// 时间复杂度O(n^2) 空间复杂度O(n)
+func canPartition(nums []int) bool {
+    sum := 0
+    for _, num := range nums {
+        sum += num
+    }
+    // 如果 nums 的总和为奇数则不可能平分成两个子集
+    if sum % 2 == 1 {
+        return false
+    }
+    
+    target := sum / 2
+    dp := make([]int, target + 1)
+
+    for _, num := range nums {
+        for j := target; j >= num; j-- {
+            if dp[j] < dp[j - num] + num {
+                dp[j] = dp[j - num] + num
+            }
+        }
+    }
+    return dp[target] == target
+}
+```
 
 ```go
 func canPartition(nums []int) bool {

problems/剑指Offer58-II.左旋转字符串.md

@@ -200,17 +200,14 @@ func reverse(b []byte, left, right int){
 JavaScript：
 
 ```javascript
-var reverseLeftWords = function (s, n) {
-    const reverse = (str, left, right) => {
-        let strArr = str.split("");
-        for (; left < right; left++, right--) {
-            [strArr[left], strArr[right]] = [strArr[right], strArr[left]];
-        }
-        return strArr.join("");
-    }
-    s = reverse(s, 0, n - 1);
-    s = reverse(s, n, s.length - 1);
-    return reverse(s, 0, s.length - 1);
+var reverseLeftWords = function(s, n) {
+  const length = s.length;
+  let i = 0;
+  while (i < length - n) {
+    s = s[length - 1] + s;
+    i++;
+  }
+  return s.slice(0, length);
 };
 ```