/* use 0-based indice*/ int lowerBound = 0; int upperBound = v.size() - 1;

while(1){

		if(lowerBound == upperBound) return v[lowerBound] == lowerBound;
		
		int i = lowerBound + (upperBound - lowerBound) / 2;
		
		if(v[i] == i){
			
			return true;
			
		}else if(v[i] < i){
			
			lowerBound = i + 1;
			
		}else if(v[i] > i){
			
			upperBound = i - 1;
			
		}
	}
}