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package class021;
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public class Code02_GetMax {
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// 输入参数：n，一定要保证，n不是1就是0
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// n == 0 -> 1
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// n == 1 -> 0
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public static int flip(int n) {
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return n ^ 1;
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}
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// 输入参数n，可以是任何一个整数
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// 如果n是非负数，返回1(int)
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// 如果n是负数，返回0(int)
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public static int sign(int n) {
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return flip((n >> 31) & 1);
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}
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// a和b中，谁大返回谁
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public static int getMax1(int a, int b) {
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int c = a - b;
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int scA = sign(c); // c >= 0 scA = 1; c < 0 scA = 0
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int scB = flip(scA);
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return a * scA + b * scB;
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}
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public static int getMax2(int a, int b) {
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int c = a - b; // c是a-b的差值，有可能溢出，也有可能不溢出
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int sa = sign(a); // a的符号，求出，a>=0 1, a<0 0
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int sb = sign(b); // b的符号，求出，b>=0 1, b<0 0
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int sc = sign(c); // c的符号，求出，c>=0 1, c<0 0
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// 如果a和b的符号，不一样，difSab == 1
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// 如果a和b的符号， 一样，difSab == 0
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int difSab = sa ^ sb;
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// 如果a和b的符号，一样，sameSab == 1
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// 如果a和b的符号，不一样，sameSab == 0
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int sameSab = flip(difSab);
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int returnA = difSab * sa + sameSab * sc;
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int returnB = flip(returnA);
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return a * returnA + b * returnB;
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}
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public static void main(String[] args) {
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int a = -16;
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int b = 1;
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System.out.println(getMax1(a, b));
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System.out.println(getMax2(a, b));
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a = 2147483647;
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b = -2147480000;
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System.out.println(getMax1(a, b)); // wrong answer because of overflow
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System.out.println(getMax2(a, b));
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}
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}
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