An array is monotonic if it is either monotone increasing or monotone decreasing.
An array A is monotone increasing if for all i <= j, A[i] <= A[j]. An array A is monotone decreasing if for all i <= j, A[i] >= A[j].
Return true if and only if the given array A is monotonic.
判断一个数组是否有序，降序升序都可以。
思路：给一个标记来记当前的数组排序方法，如果排序方法改变了，那么就不是有序的数组
public boolean isMonotonic(int[] A) {
int f=0;
for (int i = 0; i < A.length-1; i++) {
if(A[i]==A[i+1]){
continue;
}else if(A[i]<A[i+1]){
if( f == 0){
f = 1;
}else if(f==2){
return false;
}
}else if(A[i]>A[i+1]){
if( f == 0){
f = 2;
}else if(f==1){
return false;
}
}
}
return true;
}