1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
|
<<-DOC
Given a binary tree t and an integer s,
determine whether there is a root to leaf path in t
such that the sum of vertex values equals s.
Example
For
t = {
"value": 4,
"left": {
"value": 1,
"left": {
"value": -2,
"left": null,
"right": {
"value": 3,
"left": null,
"right": null
}
},
"right": null
},
"right": {
"value": 3,
"left": {
"value": 1,
"left": null,
"right": null
},
"right": {
"value": 2,
"left": {
"value": -2,
"left": null,
"right": null
},
"right": {
"value": -3,
"left": null,
"right": null
}
}
}
}
and
s = 7,
the output should be hasPathWithGivenSum(t, s) = true.
This is what this tree looks like:
4
/ \
1 3
/ / \
-2 1 2
\ / \
3 -2 -3
Path 4 -> 3 -> 2 -> -2 gives us 7, the required sum.
For
t = {
"value": 4,
"left": {
"value": 1,
"left": {
"value": -2,
"left": null,
"right": {
"value": 3,
"left": null,
"right": null
}
},
"right": null
},
"right": {
"value": 3,
"left": {
"value": 1,
"left": null,
"right": null
},
"right": {
"value": 2,
"left": {
"value": -4,
"left": null,
"right": null
},
"right": {
"value": -3,
"left": null,
"right": null
}
}
}
}
and
s = 7,
the output should be hasPathWithGivenSum(t, s) = false.
This is what this tree looks like:
4
/ \
1 3
/ / \
-2 1 2
\ / \
3 -4 -3
There is no path from root to leaf with the given sum 7.
Input/Output
[time limit] 4000ms (rb)
[input] tree.integer t
A binary tree of integers.
Guaranteed constraints:
0 ≤ tree size ≤ 5 · 104,
-1000 ≤ node value ≤ 1000.
[input] integer s
An integer.
Guaranteed constraints:
-4000 ≤ s ≤ 4000.
[output] boolean
Return true if there is a path from root to leaf in t such that the sum of node values in it is equal to s,
otherwise return false.
DOC
describe "#path_with_given_sum?" do
def leaf?(node)
node.left.nil? && node.right.nil?
end
def path_with_given_sum?(tree, target_sum)
stack = []
stack.push(tree) if tree
sum = 0
until stack.empty?
node = stack.pop
sum += node.value
return true if leaf?(node) && sum == target_sum
stack.push(node.left) if node.left
stack.push(node.right) if node.right
end
sum == target_sum
end
def path_with_given_sum?(tree, target)
return target.zero? if tree.nil?
new_target = target - tree.value
return new_target.zero? if leaf?(tree)
return true if tree.left && path_with_given_sum?(tree.left, new_target)
return true if tree.right && path_with_given_sum?(tree.right, new_target)
false
end
[
{ t: { "value": 4, "left": { "value": 1, "left": { "value": -2, "left": nil, "right": { "value": 3, "left": nil, "right": nil } }, "right": nil }, "right": { "value": 3, "left": { "value": 1, "left": nil, "right": nil }, "right": { "value": 2, "left": { "value": -2, "left": nil, "right": nil }, "right": { "value": -3, "left": nil, "right": nil } } } }, s: 7, x: true },
{ t: { "value": 4, "left": { "value": 1, "left": { "value": -2, "left": nil, "right": { "value": 3, "left": nil, "right": nil } }, "right": nil }, "right": { "value": 3, "left": { "value": 1, "left": nil, "right": nil }, "right": { "value": 2, "left": { "value": -4, "left": nil, "right": nil }, "right": { "value": -3, "left": nil, "right": nil } } } }, s: 7, x: false },
{ t: { "value": 4, "left": { "value": 1, "left": { "value": -2, "left": nil, "right": { "value": 3, "left": nil, "right": nil } }, "right": nil }, "right": { "value": 3, "left": { "value": 1, "left": { value: -1, left: nil, right: nil}, "right": nil }, "right": { "value": 2, "left": { "value": -4, "left": nil, "right": nil }, "right": { "value": -3, "left": nil, "right": nil } } } }, s: 7, x: true },
{ t: nil, s: 0, x: true },
{ t: nil, s: 1, x: false },
{ t: { "value": 5, "left": nil, "right": nil }, s: 5, x: true },
{ t: { "value": 5, "left": nil, "right": nil }, s: -5, x: false },
{ t: { "value": 5, "left": nil, "right": nil }, s: 0, x: false },
{ t: { "value": 8, "left": nil, "right": { "value": 3, "left": nil, "right": nil } }, s: 8, x: false },
].each do |x|
it do
expect(path_with_given_sum?(Tree.build_from(x[:t]), x[:s])).to eql(x[:x])
end
end
end
|
