洛谷P3957 跳房子

普及组的题.....填坑来了。

当年的我一眼二分+DP，现在都佩服起自己来了......

然后我们就写个二分，在check里面写单调队列优化DP即可。

然后就A了......

#include <cstdio>
#include <cstring>
#include <algorithm>

typedef long long LL;
const int N = 500010;
const LL INF = (1ll << 61);

int n, x[N];
LL v[N], k;

int p[N], head, top; 
LL f[N];

inline bool check(int L, int R) {
    memset(f, 0xcf, sizeof(f));
    LL ans = -INF;
    f[0] = 0;
    head = 1;
    top = 0;
    int pos_in = 0;
    for(int i = 1; i <= n; i++) {
        while(x[i] - x[pos_in] >= L) {
            p[++top] = pos_in;
            while(head < top && f[p[top]] > f[p[top - 1]]) {
                p[top - 1] = p[top];
                top--;
            }
            pos_in++;
        }
        while(head <= top && x[i] - x[p[head]] > R) {
            head++;
        }
        
        if(head <= top) {
            f[i] = f[p[head]] + v[i];
        }
        
        ans = std::max(ans, f[i]);
    }
    return ans >= k;
}

int main() {
    int d;
    LL sum = 0;
    scanf("%d%d%lld", &n, &d, &k);
    for(int i = 1; i <= n; i++) {
        scanf("%d%lld", &x[i], &v[i]);
        sum += std::max(v[i], 0ll);
    }
    if(sum < k) {
        printf("-1");
        return 0;
    }
    
    int l = 0, r = std::max(x[n] - d, d), mid;
    while(l < r) {
        mid = (l + r) >> 1;
        if(check(std::max(1, d - mid), d + mid)) {
            r = mid;
        }
        else {
            l = mid + 1;
        }
    }
    
    printf("%d", r);
    return 0;
}