【线段树】 HDOJ 5316 Magician

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线段树区间合并。。。记录奇偶的四种状态就行了。。。
#include <bits/stdc++.h>using namespace std;typedef long long LL;#define ls o << 1#define rs o << 1 | 1#define lson o << 1, L, mid#define rson o << 1 | 1, mid+1, Rconst int maxn = 100000;struct node{LL sum[2][2];}a[maxn << 2];int x[maxn];const LL INF = 1e16;int n, m;void pushup(int o){for(int i = 0; i < 2; i++)for(int j = 0; j < 2; j++)a[o].sum[i][j] = max(a[ls].sum[i][j], a[rs].sum[i][j]);for(int k = 0; k < 2; k++)for(int i = 0; i < 2; i++)for(int j = 0; j < 2; j++)a[o].sum[i][j] = max(a[o].sum[i][j], a[ls].sum[i][k] + a[rs].sum[1-k][j]);}void build(int o, int L, int R){for(int i = 0; i < 2; i++)for(int j = 0; j < 2; j++)a[o].sum[i][j] = -INF;if(L == R) {if(L % 2) a[o].sum[1][1] = x[L];else a[o].sum[0][0] = x[L];return;}int mid = (L + R) >> 1;build(lson);build(rson);pushup(o);}void update(int o, int L, int R, int q, int v){if(L == R) {for(int i = 0; i < 2; i++)for(int j = 0; j < 2; j++)a[o].sum[i][j] = -INF;if(L % 2) a[o].sum[1][1] = v;else a[o].sum[0][0] = v;return;}int mid = (L + R) >> 1;if(q <= mid) update(lson, q, v);else update(rson, q, v);pushup(o);}node query(int o, int L, int R, int ql, int qr){if(ql <= L && qr >= R) return a[o];int mid = (L + R) >> 1;node ans;memset(ans.sum, 0, sizeof ans.sum);if(qr <= mid) return query(lson, ql, qr);else if(ql > mid) return query(rson, ql, qr);else {node t1 = query(lson, ql, qr);node t2 = query(rson, ql, qr);for(int i = 0; i < 2; i++)for(int j = 0; j < 2; j++)ans.sum[i][j] = max(t1.sum[i][j], t2.sum[i][j]);for(int k = 0; k < 2; k++)for(int i = 0; i < 2; i++)for(int j = 0; j < 2; j++)ans.sum[i][j] = max(ans.sum[i][j], t1.sum[i][k] + t2.sum[1-k][j]);return ans;}}void work(){scanf("%d%d", &n, &m);for(int i = 1; i <= n; i++) scanf("%d", &x[i]);build(1, 1, n);int op, ql, qr, q, v;while(m--) {scanf("%d", &op);LL ans = -INF;if(op == 0) {scanf("%d%d", &ql, &qr);node res = query(1, 1, n, ql, qr);for(int i = 0; i < 2; i++)for(int j = 0; j < 2; j++)ans = max(ans, res.sum[i][j]);printf("%lld\n", ans);}else {scanf("%d%d", &q, &v);update(1, 1, n, q, v);}}}int main(){int _;scanf("%d", &_);while(_--) work();return 0;}
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