dp longest non-declining sequence

1  // 
2  // Created by snnnow on 2020/4/13.
 3  // 
4  // This is the basic problem of dp problem
 5  // 
6  // The longest does not drop
 7  // (Missile interception is its example)
 8  // So what is this article about,
 9  // Mainly, this question uses a two-dimensional array,
 10  // And the missile used three one-dimensional arrays at the time
 11  // In fact, it is essentially the same
 12  // (There is a structure to do it! QAQ [Manual dog head])
 13  
14  // Not much to say, ans [i] [1] is the original number
 15  // ans [i] [2] is the item The longest
 16  // ans [i] [3] points to the next (the position of the next value)
 17  //Start! 
18 #include <iostream>
 19  using  namespace std;
 20  int main () {
 21      int ans [ 10010 ] [ 10 ]; // Although we only need three numbers in the second dimension, it is better to open a larger 
22      int n;
 23      cin >> n;
 24      for ( int i = 1 ; i <= n; ++ i) {
 25          cin >> ans [i] [ 1 ];
 26          ans [i] [ 2 ] = 1 ;
 27          ans [ i] [ 3 ] =0 ;
 28  
29      }
 30      for ( int j = n- 1 ; j> = 1 ; -j) {
 31          int k = 0 ; // Note that k and p are updated every time i, so must Put in this loop here
 32          int p = 0 ;
 33          for ( int i = j + 1 ; i <= n; ++ i) {
 34  
35              if (ans [j] [ 1 ]> = ans [i] [ 1 ] && ans [j] [ 2 ]> k) { // k records the largest 
36                  k of all ans [j] [2] = ans [j] [2 ];
 37  
38                  p = j;
 39             }
 40              if (k> 0 ) {
 41                  ans [i] [ 3 ] = p; // p is a "pointer", ans [j] [3] stores a Position 
42                  ans [i] [ 2 ] = k + 1 ;
 43              }
 44  
45          }
 46  
47      }
 48      // Compare ans [i] [2] one by one to find the largest one, pay attention to find a variable and mark it 
49      int mark = 1 ;
 50      for ( int i =1 ; i <= n; i ++ ) {
 51          if (ans [i] [ 2 ]> = ans [mark] [ 2 ]) {
 52              mark = i; // This is not a sort, no double loop is needed, just find a comparison with what has been on the line 
53 is          }
 54 is      }
 55      COUT << ANS [Mark] [ 2 ] << endl;
 56 is      the while (! Mark = 0 ) {
 57 is          COUT << "  " << ANS [Mark] [ . 1 ];
 58          mark = ans [mark] [ 3 ];
 59      }
 60  return  0 ;
61 }

This time, the first reverse order loop -j is written as ++ j. . Directly fried

Then write the definition of k in the wrong place (k is updated with each ans [i])

Too silly, Xiaobai will continue to cheer!