2429. Minimize XOR

Given two positive integers num1 and num2, find the integer x such that:

• x has the same number of set bits as num2, and
• The value x XOR num1 is minimal.

Note that XOR is the bitwise XOR operation.

Return the integer x. The test cases are generated such that x is uniquely determined.

The number of set bits of an integer is the number of 1’s in its binary representation.

class Solution {
public:
    int minimizeXor(int num1, int num2) {
        int bi2 = __builtin_popcount(num2);
        int bi1 = __builtin_popcount(num1);
        if(bi2 == bi1) return num1;
        if(bi2 > bi1) {
            int res = num1, req = bi2 - bi1;
            for(int i = 0; i < 32 and req; i++) {
                if(num1 & (1<<i)) continue;
                res |= (1<<i);
                req--;
            }
            return res;
        }
        int res = 0;
        for(int i = 32; i >= 0 and bi2; i--) {
            if(num1 & (1ll<<i)) {
                res ^= (1ll<<i);
                bi2--;
            }
        }
        return res;
    }
};