【codeforces】Codeforces Round #612 (Div. 2) C. Garland——DP

Topic link
Greedy simulated for a long time, and finally gave up

Title

Give you a string from $1-$A sequence of$n$ , part of which is unknown (represented as 0). The completion sequence makes the number of
adjacent valuesopposite in parity, the least number ofadjacent values, and the opposite: two adjacent values, one of which is odd and the other is even

analysis

Greedy was used at the beginning, but the result was stuck in the twelfth example, and then changed to dp to
define the dp array as follows

int dp[120][60][2];
// dp[i][j][0/1] 表示第i+1个位置放了偶/奇数，且到第i+1处总共放了j个奇数，有多少个奇偶性相反

Get state transition equation

dp[i][j][1] = min(dp[i - 1][j - 1][0] + 1, dp[i - 1][j - 1][1]);
dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);

Of course, it depends on whether the position itself already has a value. If it is 0, both are needed. If there is already a value, perform dp according to the original value.

AC code

#include <bits/stdc++.h>

using namespace std;

void solve() {
    
    
    int n;
    int dp[120][60][2], value[120];
    cin >> n;
    for (int i = 0; i < n; ++i) {
    
    
        cin >> value[i];
    }
    memset(dp, 0x3f, sizeof(dp));
    if (value[0] == 0)
        dp[0][1][1] = dp[0][0][0] = 0;
    else
        dp[0][value[0] & 1][value[0] & 1] = 0;
    for (int i = 1; i < n; ++i) {
    
    
        for (int j = 0; j <= min(i + 1, (n + 1) / 2); ++j) {
    
    
            if ((value[i] & 1 || value[i] == 0) && j > 0)
                dp[i][j][1] = min(dp[i - 1][j - 1][0] + 1, dp[i - 1][j - 1][1]);
            if (!(value[i] & 1))
                dp[i][j][0] = min(dp[i - 1][j][1] + 1, dp[i - 1][j][0]);
        }
    }
    cout << min(dp[n - 1][(n + 1) / 2][1], dp[n - 1][(n + 1) / 2][0]) << endl;
}

int main() {
    
    
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
#ifdef ACM_LOCAL
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
    long long test_index_for_debug = 1;
    char acm_local_for_debug;
    while (cin >> acm_local_for_debug) {
    
    
        cin.putback(acm_local_for_debug);
        if (test_index_for_debug > 20) {
    
    
            throw runtime_error("Check the stdin!!!");
        }
        auto start_clock_for_debug = clock();
        solve();
        auto end_clock_for_debug = clock();
        cout << "Test " << test_index_for_debug << " successful" << endl;
        cerr << "Test " << test_index_for_debug++ << " Run Time: "
             << double(end_clock_for_debug - start_clock_for_debug) / CLOCKS_PER_SEC << "s" << endl;
        cout << "--------------------------------------------------" << endl;
    }
#else
    solve();
#endif
    return 0;
}