USACO 2009 Mar Silver 3.Look Up

Description

Farmer John's N (1 <= N <= 100,000) cows, conveniently numbered
1..N, are once again standing in a row. Cow i has height H_i (1 <=
H_i <= 1,000,000).

Each cow is looking to her left toward those with higher index
numbers. We say that cow i 'looks up' to cow j if i < j and H_i <
H_j. For each cow i, FJ would like to know the index of the first
cow in line looked up to by cow i.

Note: about 50% of the test data will have N <= 1,000.

Input

* Line 1: A single integer: N

* Lines 2..N+1: Line i+1 contains the single integer: H_i

Output

* Lines 1..N: Line i contains a single integer representing the
        smallest index of a cow up to which cow i looks. If no such
        cow exists, print 0.

Sample Input

6

3

2

6

1

1

2

Sample Output

3

3

0

6

6

0

HINT

INPUT DETAILS:

FJ has six cows of heights 3, 2, 6, 1, 1, and 2.

OUTPUT DETAILS:

Cows 1 and 2 both look up to cow 3; cows 4 and 5 both look up to cow 6; and
cows 3 and 6 do not look up to any cow.

求距离此点最近且比它高的点

可以用单调栈维护

有高的点直接比较大小之后赋值编号

#include<stdio.h>
int a[100001],s[100001],ans[100001],i,top;
int main()
{
	int n;
	scanf("%d",&n);
	for(i=1;i<=n;i++)
		scanf("%d",&a[i]);
	for(i=n;i>=0;i--)
	{
		while(top&&a[s[top]]<=a[i])
			top--;
		ans[i]=s[top];
		s[++top]=i;
	}	
	for(i=1;i<=n;i++)
		printf("%d\n",ans[i]);
}