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Author: Chris Wu

problems/binary-search.py

@@ -42,3 +42,29 @@ def search(self, nums, target):
         #check if target in `nums`
         if nums[i]==target: return i
         else: return -1
+
+
+# 2020/7/19
+class Solution(object):
+    def search(self, nums, target):
+        if not nums: return -1
+
+        l = 0
+        r = len(nums)-1
+
+        while True:
+            if l>r: break
+            if target<nums[l]: return -1
+            if nums[r]<target: return -1
+
+            if target==nums[l]: return l
+            if target==nums[r]: return r
+
+            m = (l+r)/2
+            if target==nums[m]:
+                return m
+            elif target<nums[m]:
+                r = m-1
+            else:
+                l = m+1
+        return -1

problems/distribute-coins-in-binary-tree.py

@@ -0,0 +1,20 @@
+class Solution(object):
+    def distributeCoins(self, root):
+        def count_moves(node):
+            if not node: return 0
+            l, r = count_moves(node.left), count_moves(node.right)
+            self.moves += abs(l)+abs(r)
+            return node.val-1+l+r
+
+        self.moves = 0
+        count_moves(root)
+        return self.moves
+
+"""
+If the leaf of a tree has 0 coins (an excess of -1 from what it needs), then we should push a coin from its parent onto the leaf.
+If it has say, 4 coins (an excess of 3), then we should push 3 coins off the leaf.
+In total, the number of moves from that leaf to or from its parent is excess = Math.abs(num_coins - 1).
+Afterwards, we never have to consider this leaf again in the rest of our calculation.
+
+`count_moves(node)` count the node.left and node.right moves and return the excess number of coins in the subtree at or below this node.
+"""

problems/find-first-and-last-position-of-element-in-sorted-array.py

@@ -48,3 +48,45 @@ def searchRange(self, nums, target):
         if nums[l]!=target or nums[r-1]!=target: return [-1, -1] #check if target in `nums`
         return [l, r-1]
 
+
+#2020/7/19
+class Solution(object):
+    def searchRange(self, nums, target):
+        def find_range(i, nums):
+            start = end = i
+            while 0<=start-1 and nums[start-1]==nums[i]:
+                start -= 1
+            while end+1<len(nums) and nums[end+1]==nums[i]:
+                end += 1
+            return [start, end]
+            
+        
+        if not nums: return [-1, -1]
+        l = 0
+        r = len(nums)-1
+
+        while True:
+            if l>r: break
+            if target<nums[l]: return [-1, -1]
+            if target>nums[r]: return [-1, -1]
+
+            if target==nums[l]: return find_range(l, nums)
+            if target==nums[r]: return find_range(r, nums)
+
+            m = (l+r)/2
+            if target==nums[m]:
+                return find_range(m, nums)
+            elif target<nums[m]:
+                r = m-1
+            else:
+                l = m+1
+        
+        return [-1, -1]
+
+
+
+
+
+
+
+

problems/house-robber-iii.py

@@ -30,4 +30,5 @@ def get_max_value(node):
 
             return rob, not_rob
 
-        return max(get_max_value(root))
+        return max(get_max_value(root))
+        

problems/search-insert-position.py

@@ -47,3 +47,35 @@ def searchInsert(self, nums, target):
             return l
         else:
             return l+1
+
+
+#2020/7/19
+class Solution(object):
+    def searchInsert(self, nums, target):
+        if not nums: return 0
+        
+        l = 0
+        r = len(nums)-1
+        
+        while True:
+            if l>r: break
+            if target<nums[l]: return l
+            if target>nums[r]: return r+1
+            
+            if target==nums[l]: return l
+            if target==nums[r]: return r
+            
+            m = int((l+r)/2)
+            
+            if target==nums[m]:
+                return m
+            elif target>nums[m]:
+                l = m+1
+            else:
+                r = m-1
+        return 0
+
+
+
+
+