10739: ABC136 - C - Build Stairs
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Description
There are $N$ squares arranged in a row from left to right. The height of the $i$-th square from the left is $H_i$.
For each square, you will perform either of the following operations once:
- Decrease the height of the square by $1$.
- Do nothing.
Determine if it is possible to perform the operations so that the heights of the squares are non-decreasing from left to right.
For each square, you will perform either of the following operations once:
- Decrease the height of the square by $1$.
- Do nothing.
Determine if it is possible to perform the operations so that the heights of the squares are non-decreasing from left to right.
Input
There are $N$ squares arranged in a row from left to right. The height of the $i$-th square from the left is $H_i$.
For each square, you will perform either of the following operations once:
- Decrease the height of the square by $1$.
- Do nothing.
Determine if it is possible to perform the operations so that the heights of the squares are non-decreasing from left to right.
For each square, you will perform either of the following operations once:
- Decrease the height of the square by $1$.
- Do nothing.
Determine if it is possible to perform the operations so that the heights of the squares are non-decreasing from left to right.
Output
If it is possible to perform the operations so that the heights of the squares are non-decreasing from left to right, print `Yes`; otherwise, print `No`.
Constraints
- All values in input are integers.
- $1 \leq N \leq 10^5$
- $1 \leq H_i \leq 10^9$
- $1 \leq N \leq 10^5$
- $1 \leq H_i \leq 10^9$
Sample 1 Input
5
1 2 1 1 3
Sample 1 Output
Yes
You can achieve the objective by decreasing the height of only the second square from the left by $1$.
Sample 2 Input
4
1 3 2 1
Sample 2 Output
No
Sample 3 Input
5
1 2 3 4 5
Sample 3 Output
Yes
1
1000000000
Yes