用map记录nums2里面每一个元素的下标
然后遍历nums1 从下标位置的下一个元素开始找
class Solution {
public:
vector<int> nextGreaterElement(vector<int>& nums1, vector<int>& nums2) {
map<int,int> mp;
for( int i=0;i<nums2.size();i++){
mp[ nums2[i] ] = i;
}
vector<int> ret;
for( int i=0;i<nums1.size();i++){
int pos = mp[ nums1[i] ];
bool is = false;
for( int j = pos+1;j < nums2.size();j ++ ){
if( nums2[j] > nums1[i] ){
ret.push_back( nums2[j] );
is = true;
break;
}
}
if(!is){
ret.push_back( -1 );
}
}
return ret;
}
};
单调栈
class Solution {
public:
vector<int> nextGreaterElement(vector<int>& nums1, vector<int>& nums2) {
stack<int> st;
map<int,int> mp;
for( int i = 0;i < nums2.size();i ++){
if( st.empty() ){
st.push( nums2[i] );
}else{
int stop = st.top();
if( nums2[i] < stop ){
st.push( nums2[i] );
}else if(nums2[i] > stop){
while( !st.empty() && st.top() < nums2[i] ){
mp[ st.top()] = nums2[i];
st.pop();
}
st.push( nums2[i] );
}
}
}
while( !st.empty() ){
mp[ st.top()] = -1;
st.pop();
}
vector<int> ret;
for( auto i: nums1 ){
if( mp[i]!=0 ){
ret.push_back( mp[i] );
}else{
ret.push_back( -1 );
}
}
return ret;
}
};