Hdu oj 2141

Question address: http://acm.hdu.edu.cn/showproblem.php? PID = 1, 2141

The key to solving the problem is to convert the judgment A + B + C = x to a + B = x-C, calculate all the combinations of A + B, and then quickly rank and perform binary search.

After optimization, C is also sorted, which can reduce the search space continuously in the search, but it does not seem to be much faster. BelowCode

# Include <cstdio> <br/> # include <cstdlib> <br/> # include <iostream> <br/> using namespace STD; </P> <p> // # define test </P> <p> int a_array [500]; <br/> int a_array_len; </P> <p> int B _array [500]; <br/> int B _array_len; </P> <p> int c_array [500]; <br/> int c_array_len; </P> <p> long d_array [500]; <br/> int d_array_len; </P> <p> long sum_array [250000]; <br/> int sum_array_len; </P> <p> int CMP (const void * a, const voi D * B) <br/>{< br/> long s = * (int *) A-* (int *) B; <br/> If (S> 0) return 1; <br/> If (S = 0) return 0; <br/> If (S <0) return-1; <br/>}</P> <p> int cmpc (const void * a, const void * B) <br/> {<br/> long s = * (int *) B-* (int *) A; <br/> If (S> 0) return 1; <br/> If (S = 0) return 0; <br/> If (S <0) Return-1; <br/>}</P> <p> void prepare () <br/>{< br/> sum_array_len = 0; </P> <p> for (int I = 0; I <a_array_len; ++ I) {<br/> for (Int J = 0; j <B _array_len; ++ J) {<br/> sum_array [sum_array_len ++] = a_array [I] + B _array [J]; <br/>}</P> <p> # ifdef test </P> <p> printf ("test log: \ n "); <br/> for (INT I = 0; I <sum_array_len; ++ I) cout <sum_array [I] <","; <br/> printf ("\ n"); </P> <p> # endif </P> <p> qsort (sum_array, sum_array_len, sizeof (sum_array [0]), CMP); <br/> qsort (c_array, c_array_len, siz EOF (c_array [0]), cmpc); <br/> # ifdef test </P> <p> printf ("test log: \ n "); <br/> for (INT I = 0; I <sum_array_len; ++ I) cout <sum_array [I] <","; <br/> printf ("\ n"); <br/> for (INT I = 0; I <c_array_len; ++ I) printf ("% d ,", c_array [I]); <br/> printf ("\ n "); </P> <p> # endif </P> <p >}</P> <p> bool judge (const Int & X) <br/> {<br/> for (INT I = 0; I <c_array_len; ++ I) {<br/> d_array [I] = x-c_array [I]; <br/>}</P> <p> Int low = 0; <br/> int high = sum_array_len-1; <br/> int center; </P> <p> for (INT I = 0; I <d_array_len; ++ I) {<br/> while (high> = low) {<br/> center = (low + high)/2; <br/> If (sum_array [center] = d_array [I]) return true; <br/> If (sum_array [center]> d_array [I]) {<br/> high = center-1; <br/>} else {<br/> low = center + 1; <br/>}</P> <p> low = center; <br/> high = sum_array_len-1; <B R/>}</P> <p> return false; <br/>}</P> <p> int maxinarray (INT array [], const Int & Len) <br/>{< br/> int max = array [0]; </P> <p> for (INT I = 1; I <Len; ++ I) {<br/> If (array [I]> MAX) max = array [I]; <br/>}</P> <p> return Max; <br/>}</P> <p> int mininarray (INT array [], const Int & Len) <br/>{< br/> int min = array [0]; </P> <p> for (INT I = 1; I <Len; ++ I) {<br/> If (array [I] <min) min = array [I]; <br/>}</P> <p> Return min; <br/>}</P> <p> inline void Yes () <br/> {<br/> printf ("Yes \ n "); <br/>}</P> <p> inline void no () <br/>{< br/> printf ("NO \ n "); <br/>}</P> <p> int main () <br/> {<br/> int case_count = 0; </P> <p> while (scanf ("% d", & a_array_len, & B _array_len, & c_array_len )! = EOF) {<br/> printf ("case % d: \ n", ++ case_count); <br/> d_array_len = c_array_len; </P> <p> for (INT I = 0; I <a_array_len; ++ I) {<br/> scanf ("% d", a_array + I ); <br/>}</P> <p> for (INT I = 0; I <B _array_len; ++ I) {<br/> scanf ("% d ", B _array + I); <br/>}</P> <p> for (INT I = 0; I <c_array_len; ++ I) {<br/> scanf ("% d", c_array + I); <br/>}</P> <p> int x_count; <br/> scanf ("% d", & x_count); <br/>/* bool prepared = false; <Br/> long max_sum = maxinarray (a_array, a_array_len) + maxinarray (B _array, B _array_len) <br/> + maxinarray (c_array, c_array_len ); <br/> long min_sum = mininarray (a_array, a_array_len) + mininarray (B _array, B _array_len) <br/> + mininarray (c_array, c_array_len ); */<br/> prepare (); <br/> for (INT I = 0; I <x_count; ++ I) {<br/> int X; <br/> scanf ("% d", & X); <br/>/* If (x> max_sum) {<br/> NO (); <Br/> continue; <br/>} else if (x <min_sum) {<br/> NO (); <br/> continue; <br/>}< br/> If (! Prepared) {<br/> prepare (); <br/> prepared = true; <br/>}*/<br/> bool result = judge (X ); <br/> If (result) {<br/> Yes (); <br/>}else {<br/> NO (); <br/>}</P> <p> return 0; <br/>}
In my opinion, the comments are "obviously correct" pruning, But wa does not understand why.

The bad thing is that the judge function once forgot to write return false, which wasted a lot of time, and GCC didn't report warning! I don't know how to raise the warning level in the command line. I 'd like to hear it.