DP—最长下降子序列（代码）

原理和最长上升子序列一样，排序和二分时比较方法改一下即可

#include <iostream>#include <cstring>int arr[1003],ans[1003];using namespace std;int binary_search(int i,int len){    int left,right,mid;    left = 0,right = len;    while(left < right){        mid = left + (right - left) / 2;        if(ans[mid] <= arr[i])            right = mid;        else            left = mid + 1;    }    return left;}int main(){    int n;    while(cin >> n){        int len = 1;        for(int i = 1;i <= n;i++)            cin >> arr[i];        ans[1] = arr[1];        for(int i = 2;i <= n;i++){            if(arr[i] < ans[len])                ans[++len] = arr[i];            else{                int pos = binary_search(i, len);                ans[pos] = arr[i];            }        }        cout << len <<endl;        for(int i = 1;i <= len;i++)            cout << ans[i] << " ";    }}