foj1465 Sub Sequence 記錄

這道題目感覺也不是很難，奈何提交多次都是超時，後來發現原來會卡STL的sort……先把超時的程序貼出來吧，這道題目也讓我知道了原來全局區的大小可以比棧多許多。

//解題思路
//用sum[j] = v[0] + .. + v[j]
//如果v[x]都是正數，則很容易解決，因爲直接for j，然後可以用2分的思想；
//問題在於v[x]可以<0, 因此得到的結果sum不一定是有序的;
//改進思路：
//可以對sum數組進行排序於是得到有序數組
//sum[0], sum[1], sum[2], ..., sum[n]
//分情況討論，如果目標值m<0,那麼就按照從大到小排序，否則從小到大排序
//if sum[j]-sum[i]=dest, and sum[j].index>sum[i].index即可，
//else if (sum[mid] - sum[i] < dest) low, high
//else if (sum[j] - sum[i] > dest)

#include <iostream> #include <cstdio> #include <algorithm> using namespace std; const int MAXN = 1000000; typedef int key_t; struct Node { Node() { } Node(const Node &other) { this->index = other.index; this->value = other.value; } int index; key_t value; }; inline bool lessComparer(const Node &lhs, const Node &rhs) { return lhs.value < rhs.value || (lhs.value == rhs.value && lhs.index < rhs.index); } inline bool greaterComparer(const Node &lhs, const Node &rhs) { return lhs.value > rhs.value || (lhs.value == rhs.value && lhs.index < rhs.index); } Node nodes[MAXN]; int n, m; int searchWhenMGreaterEqualZero() { int nCount = 0; for (int i = 0; i < n; ++i) { if (nodes[i].value == m) ++nCount; int low = i + 1, high = n - 1; int mid; while (low <= high) { mid = (low + high) >> 1; key_t diff = nodes[mid].value - nodes[i].value; if (diff == m) { if (nodes[mid].index > nodes[i].index) { ++nCount; } int prev = mid - 1; while (prev > i && nodes[prev].value == nodes[mid].value) { if (nodes[prev].index > nodes[i].index) ++nCount; --prev; } int post = mid + 1; while (post < n && nodes[mid].value == nodes[post].value) { if (nodes[post].index > nodes[i].index) ++nCount; ++post; } break; } else if (diff < m) { low = mid + 1; } else { high = mid - 1; } } } return nCount; } int searchWhenMLessZero() { int nCount = 0; for (int i = 0; i < n; ++i) { if (nodes[i].value == m) ++nCount; int low = i + 1, high = n - 1; int mid; while (low <= high) { mid = (low + high) >> 1; key_t diff = nodes[mid].value - nodes[i].value; if (diff == m) { if (nodes[mid].index > nodes[i].index) { ++nCount; } int prev = mid - 1; while (prev > i && nodes[prev].value == nodes[mid].value) { if (nodes[prev].index > nodes[i].index) ++nCount; --prev; } int post = mid + 1; while (post < n && nodes[mid].value == nodes[post].value) { if (nodes[post].index > nodes[i].index) ++nCount; ++post; } break; } else if (diff < m) { high = mid - 1; } else { low = mid + 1; } } } return nCount; } int main() { //freopen("G:/acm/foj1465.txt", "r", stdin); int nCase; scanf("%d", &nCase); while (nCase-- > 0) { scanf("%d %d", &n, &m); int temp; scanf("%d", &temp); nodes[0].value = temp; nodes[0].index = 0; for (int i = 1; i < n; ++i) { scanf("%d", &temp); nodes[i].value = nodes[i - 1].value + temp; nodes[i].index = i; } int nCount = 0; if (m >= 0) { sort(nodes, nodes + n, lessComparer); nCount = searchWhenMGreaterEqualZero(); } else { sort(nodes, nodes + n, greaterComparer); nCount = searchWhenMLessZero(); } printf("%d/n", nCount); } }