hdu 4105 Electric wave (dp)

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题目链锁：http://acm.hdu.edu.cn/showproblem.php?pid=4105

题意：给出一串数字，最多能插入多少个空格使它变成电波的形式

dp[i][j][0]表示把i到j作为波谷时最多能插入多少个空格，dp[i][j][1]表示i到j作为波峰时最多能插入多少个空格

#include<iostream>#include<cstring>#include<string>#include<cstdio>#include<stdio.h>#include<algorithm>#include<cmath>#include<set>#include<map>#include<queue>#include<vector>using namespace std;#define inf 0x3f3f3f3f#define eps 1e-9#define mod 1000000007#define FOR(i,s,t) for(int i = s; i < t; ++i )#define REP(i,s,t) for( int i = s; i <= t; ++i )#define LL long long#define ULL unsigned long long#define pii pair<int,int>#define MP make_pair#define lson id << 1 , l , m#define rson id << 1 | 1 , m + 1 , r #define maxn ( 400 + 10 )#define maxe ( 50000+10 )int dp[111][111][2], a[111];int cmp ( int i, int j, int l, int r ) {    while( a[i] == 0 && i < j ) ++i ;    while( a[l] == 0 && l < r ) ++l;    if( j - i < r - l ) return 0;    if( j - i > r - l ) return 1;    while( i <= j ) {        if( a[i] > a[l] ) return 1;        if( a[i] < a[l] ) return 0;        ++i, ++l;    }    return -1;}char s[111];int main () {    int n;    while( scanf("%d", &n ) != EOF ) {        scanf("%s", s );        for( int i = 0 ; i < n; i++ )            a[i] = s[i]-'0';        memset( dp, 0, sizeof( dp ) );        //for( int i = 0; i < n; i++ )            //dp[i][n-1][0] = dp[i][n-1][1] = 1;        for( int i = n-2; i >= 0; i-- ) {            for( int j = i; j < n-1; j++ ) {                int l = j + 1;                for( int r = l; r < n; r++ ) {                    int temp = cmp( i, j, l, r );                    if( temp == 1 )                         dp[i][j][1] = max( dp[i][j][1], dp[l][r][0] + 1 );                    if( temp == 0 )                        dp[i][j][0] = max( dp[i][j][0], dp[l][r][1] + 1 );                }            }        }        int ans = 0;        for( int i = 0 ; i < n; i++ )            ans = max( ans, dp[0][i][0] );        printf( "%d\n", ans );    }    return 0;}

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