Question

用java编写应用程序，求1*1-2*2+3*3-4*4+...+97*97-98*98+99*99-100*100的值

Answer 1

public class TT {
public static void main(String[] args) {
method1();//方法1
method2();//方法2
}

public static void method1() {
int sum = 0;
for (int i = 1; i <= 100; i++) {
int temp = 0;
if (i%2==0) {
temp = (-i*i);
System.out.print("-"+i+"*"+i);
}
else {
temp = (i*i);
System.out.print("+"+i+"*"+i);
}
sum += temp;
}
System.out.println("="+sum);
}

public static void method2() {
int sum = 0;
for (int i = 1; i <= 100; i++) {
sum+=(i%2==0)?(-i*i):(i*i);
}
System.out.println(sum);
}
}
输出结果：+1*1-2*2+3*3-4*4+5*5-6*6+7*7-8*8+9*9-10*10+11*11-12*12+13*13-14*14+15*15-16*16+17*17-18*18+19*19-20*20+21*21-22*22+23*23-24*24+25*25-26*26+27*27-28*28+29*29-30*30+31*31-32*32+33*33-34*34+35*35-36*36+37*37-38*38+39*39-40*40+41*41-42*42+43*43-44*44+45*45-46*46+47*47-48*48+49*49-50*50+51*51-52*52+53*53-54*54+55*55-56*56+57*57-58*58+59*59-60*60+61*61-62*62+63*63-64*64+65*65-66*66+67*67-68*68+69*69-70*70+71*71-72*72+73*73-74*74+75*75-76*76+77*77-78*78+79*79-80*80+81*81-82*82+83*83-84*84+85*85-86*86+87*87-88*88+89*89-90*90+91*91-92*92+93*93-94*94+95*95-96*96+97*97-98*98+99*99-100*100=-5050
-5050

Answer 2

public class Test{
public static void main (String[] args){
int result=0;
for(int i=1;i<=100;i++){
if(i%2==0)
result-=i*i;
else
result+=i*i;
}
System.out.print(result);
}
}

Answer 3

public class Sum {

public static void main(String[] args) {

int i = 1;
int sum = 0;

while(i <= 100){
if(i % 2 == 0){
sum = sum - i *i;
}else{
sum = sum + i * i;
}

i++;
}

System.out.println("1*1-2*2+3*3-4*4+...+97*97-98*98+99*99-100*100 = " + sum);
}

}

--------------------testing
1*1-2*2+3*3-4*4+...+97*97-98*98+99*99-100*100 = -5050

Answer 4

sum = 0
sign = -1
for i in range(1, 101):
sign *= -1
sum += i * i * sign
print(sum)

python版的，答案是-5050，这是巧合？

Answer 5

class test{
public static void main(String[] args) {
int sum = 0;
for(int i=1;i<=100;i++){
if(i%2 != 0)
sum += i*1;
else
sum -= i*i;
}
System.out.println(sum);
}
}