Validate Stack Sequences
Given two sequences pushed
and popped
with distinct values, return true
if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.
Example 1:
Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
Output: true
Explanation: We might do the following sequence:
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1
Example 2:
Input: pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
Output: false
Explanation: 1 cannot be popped before 2.
Note:
0 <= pushed.length == popped.length <= 1000
0 <= pushed[i], popped[i] < 1000
pushed
is a permutation ofpopped
.pushed
andpopped
have distinct values.
class Solution {
public boolean validateStackSequences(int[] pushed, int[] popped) {
int i = 0, j = 0;
Deque<Integer> st = new LinkedList<>();
while (i < pushed.length || j < popped.length) {
// Pop if you can
if (st.size() != 0 && st.peek() == popped[j]) {
st.pop();
j++;
}
// Else try to push
else if (i < pushed.length) {
st.push(pushed[i]);
i++;
} else
break;
}
return st.size() == 0;
}
}
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