C code

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C practice

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#include <stdio.h>

int fib(int N);

int main() {
    int res = fib(5);
    printf("res is %d\n", res);
}

// approach 1
int fib(int N){
    if (N <= 1) {
        return N;
    }
    int lib[N + 1];
    lib[0] = 0;
    lib[1] = 1;
    for (int i = 2; i <= N; i++) {
        lib[i] = lib[i - 1] + lib[i - 2];
    }        
    return lib[N];
}

// approach 2
int fib2(int N){
    if (N <= 1)
        return N;
    return fib(N - 1) + fib(N - 2);
}
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#include <stdio.h>
#include <math.h>
#include <ctype.h>

int myAtoi(char * str);

int main() {
    int res = myAtoi("   42  ");
    printf("res is %d\n", res);
}

int myAtoi(char * str){
    int i = 0, sign = 1;
    while (str[i] == ' ') {
        i += 1;
    }
    
    if (str[i] == '+')
        i += 1;
    else if (str[i] == '-') {
        i += 1;
        sign = -1;        
    }

    long res = 0;
    while (isdigit(str[i])) {
        res = res * 10 + str[i] - '0';
        
        if (sign * res >= pow(2, 31) - 1) {
            return pow(2, 31) - 1;
        } else if (sign * res <= pow(2,31) * (-1)) {
            return pow(2, 31) * (-1);
        }
        i += 1;
    }
    
    return (int)res * sign;
}
  • 191. Number of 1 Bits bit operation 
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    int hammingWeight(uint32_t n) {
        int res = 0;
        while (n > 0) {
            res += n & 1;
            n = n >> 1;
        }
        return res;
    }
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