updates

Author: wuduhren

problems/python3/binary-search.py

@@ -0,0 +1,16 @@
+class Solution:
+    def search(self, nums: List[int], target: int) -> int:
+        l = 0
+        r = len(nums)-1
+        
+        while l<=r:
+            m = l + int((r-l)/2)
+            
+            if nums[m]>target:
+                r = m-1
+            elif nums[m]<target:
+                l = m+1
+            else:
+                return m
+        
+        return -1

problems/python3/n-queens.py

@@ -0,0 +1,45 @@
+class Solution:
+    def solveNQueens(self, n: int) -> List[List[str]]:
+        def helper(row: int):
+            if row==n:
+                ans.append(convertFormat(queenCols))
+                return
+            
+            for col in range(n):
+                posDiag = row+col
+                negDiag = row-col
+                
+                if col in colUsed or posDiag in posDiagUsed or negDiag in negDiagUsed: continue
+                
+                queenCols.append(col)
+                colUsed.add(col)
+                posDiagUsed.add(posDiag)
+                negDiagUsed.add(negDiag)
+                
+                helper(row+1)
+                
+                queenCols.pop()
+                colUsed.remove(col)
+                posDiagUsed.remove(posDiag)
+                negDiagUsed.remove(negDiag)
+        
+        def convertFormat(queenCols: List[int]) -> List[str]:
+            output = []
+            for col in queenCols:
+                row = ''
+                for i in range(n):
+                    if i==col:
+                        row += 'Q'
+                    else:
+                        row += '.'
+                output.append(row)
+            return output
+            
+        ans = []
+        queenCols = []
+        colUsed = set()
+        posDiagUsed = set()
+        negDiagUsed = set()
+        
+        helper(0)
+        return ans

problems/python3/search-a-2d-matrix.py

@@ -0,0 +1,22 @@
+class Solution:
+    def searchMatrix(self, matrix: List[List[int]], target: int) -> bool:
+        N = len(matrix)
+        M = len(matrix[0])
+        
+        l = 0
+        r = N*M-1
+        
+        while l<=r:
+            m = l + int((r-l)/2)
+            
+            i = int(m/M)
+            j = m%M
+            
+            if matrix[i][j]<target:
+                l = m+1
+            elif matrix[i][j]>target:
+                r = m-1
+            else:
+                return True
+        
+        return False