和I相比有了单点更新，所以不能只记录一个前缀和，而是要在线段树上多维护一个sum，表示这个结点的区间和，然后其他的就和I一样了。
1 #include <iostream> 2 #include <cstring> 3 #include <cstdio> 4 using namespace std; 5 6 const int N = 50001; 7 int a[N]; 8 9 struct Node 10 { 11 int l, r, sum; 12 int maxl, maxr, maxn; 13 } node[N << 2]; 14 15 void pushup( int i ) 16 { 17 int lc = i << 1, rc = lc | 1; 18 node[i].sum = node[lc].sum + node[rc].sum; 19 node[i].maxl = max( node[lc].maxl, node[lc].sum + node[rc].maxl ); 20 node[i].maxr = max( node[rc].maxr, node[rc].sum + node[lc].maxr ); 21 node[i].maxn = max( node[lc].maxn, node[rc].maxn ); 22 node[i].maxn = max( node[i].maxn, node[lc].maxr + node[rc].maxl ); 23 } 24 25 void build( int i, int l, int r ) 26 { 27 node[i].l = l, node[i].r = r; 28 if ( l == r ) 29 { 30 node[i].sum = node[i].maxl = node[i].maxr = node[i].maxn = a[l]; 31 return ; 32 } 33 int lc = i << 1, rc = lc | 1, mid = ( l + r ) >> 1; 34 build( lc, l, mid ); 35 build( rc, mid + 1, r ); 36 pushup(i); 37 } 38 39 void update( int i, int pos, int val ) 40 { 41 if ( node[i].l == pos && node[i].r == pos ) 42 { 43 node[i].sum = node[i].maxl = node[i].maxr = node[i].maxn = val; 44 return ; 45 } 46 int mid = ( node[i].l + node[i].r ) >> 1; 47 if ( pos <= mid ) 48 { 49 update( i << 1, pos, val ); 50 } 51 else 52 { 53 update( i << 1 | 1, pos, val ); 54 } 55 pushup(i); 56 } 57 58 Node query( int i, int l, int r ) 59 { 60 if ( node[i].l == l && node[i].r == r ) 61 { 62 return node[i]; 63 } 64 int lc = i << 1, rc = lc | 1, mid = ( node[i].l + node[i].r ) >> 1; 65 if ( r <= mid ) 66 { 67 return query( lc, l, r ); 68 } 69 else if ( l > mid ) 70 { 71 return query( rc, l, r ); 72 } 73 else 74 { 75 Node ln = query( lc, l, mid ), rn = query( rc, mid + 1, r ), res; 76 res.sum = ln.sum + rn.sum; 77 res.maxl = max( ln.maxl, ln.sum + rn.maxl ); 78 res.maxr = max( rn.maxr, rn.sum + ln.maxr ); 79 res.maxn = max( ln.maxn, rn.maxn ); 80 res.maxn = max( res.maxn, ln.maxr + rn.maxl ); 81 return res; 82 } 83 } 84 85 int main () 86 { 87 int n, m; 88 while ( scanf("%d", &n) != EOF ) 89 { 90 for ( int i = 1; i <= n; i++ ) 91 { 92 scanf("%d", a + i); 93 } 94 build( 1, 1, n ); 95 scanf("%d", &m); 96 while ( m-- ) 97 { 98 int op, x, y; 99 scanf("%d%d%d", &op, &x, &y); 100 if ( op == 0 ) 101 { 102 update( 1, x, y ); 103 } 104 else 105 { 106 Node tmp = query( 1, x, y ); 107 printf("%d ", tmp.maxn); 108 } 109 } 110 } 111 return 0; 112 }