线段树。
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 using namespace std; 5 6 #define mymax(a, b) (a>b) ? a:b 7 8 const int maxn = 200005; 9 10 int nums[maxn<<2]; 11 12 void PushUP(int rt) { 13 nums[rt] = mymax(nums[rt<<1], nums[rt<<1|1]); 14 } 15 16 void build(int l, int r, int rt) { 17 if (l == r) { 18 scanf("%d", &nums[rt]); 19 return ; 20 } 21 int mid = (l+r)>>1; 22 build(l, mid, rt<<1); 23 build(mid+1, r, rt<<1|1); 24 PushUP(rt); 25 } 26 27 int query(int ll, int rr, int l, int r, int rt) { 28 if (ll <= l && rr>= r) 29 return nums[rt]; 30 int mid = (l+r)>>1; 31 int max = -1, tmp = -1; 32 if (ll <= mid) { 33 max = query(ll, rr, l, mid, rt<<1); 34 } 35 if (rr > mid) { 36 tmp = query(ll, rr, mid+1, r, rt<<1|1); 37 if (tmp > max) 38 max = tmp; 39 } 40 return max; 41 } 42 43 void update(int des, int val, int l, int r, int rt) { 44 if (l == r) { 45 nums[rt] = val; 46 return ; 47 } 48 int mid = (l+r)>>1; 49 if (des <= mid) 50 update(des, val, l, mid, rt<<1); 51 else 52 update(des, val, mid+1, r, rt<<1|1); 53 PushUP(rt); 54 } 55 56 int main() { 57 int n, m; 58 int i, j; 59 char cmd[3]; 60 61 while (scanf("%d %d", &n, &m) != EOF) { 62 build(1, n, 1); 63 while (m--) { 64 scanf("%*c%s %d %d", cmd, &i, &j); 65 if (cmd[0] == 'Q') 66 printf("%d ", query(i,j,1,n,1)); 67 else 68 update(i,j,1,n,1); 69 } 70 } 71 72 return 0; 73 }