codeforce 251 A(二分或者尺取法或者单调队列)

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二分

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;#define LL long longconst int maxn = 1e5+100;LL a[maxn];int main(){    LL n, d;    while(scanf("%I64d%I64d", &n, &d) != EOF){        for(int i = 0; i < n; i++) scanf("%I64d", &a[i]);        LL ans = 0;        for(int i = 1; i < n; i++){            LL j = i - (lower_bound(a, a+i, a[i]-d)-a);            ans += (j-1)*j/2;        }        printf("%I64d\n", ans);    }    return 0;}

尺取法

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;#define LL long longconst int maxn = 1e5+100;LL a[maxn];//尺取法int main(){    LL n, d;    while(scanf("%I64d%I64d", &n, &d) != EOF){        for(int i = 0; i < n; i++) scanf("%I64d", &a[i]);        LL ans = 0;        LL j = 0;        for(int i = 0; i < n; i++){            while(j < n && a[j] - a[i] <= d) j++;  //          printf("j = %I64d\n", j);            ans += (j-i-1)*(j-i-2)/2;        }        printf("%I64d\n", ans);    }    return 0;}

单调队列

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;#define LL long longconst int maxn = 1e5+100;LL a[maxn], que[maxn];int main(){    LL n, d;    while(scanf("%I64d%I64d", &n, &d) != EOF){        for(int i = 0; i < n; i++) scanf("%I64d", &a[i]);        if(n < 3){ printf("0\n"); continue;}        LL ans = 0;        LL head = 0, tail = 0;        while(head <= tail){            while(a[tail] - a[head] <= d && tail < n) que[tail] = a[tail], tail++;            head++;  //          printf("head = %I64d, tail = %I64d\n", head, tail);            if(head < n) ans += (tail-head)*(tail-head-1)/2;        }        printf("%I64d\n", ans);    }    return 0;}

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